Gating scheme for wireless communication over unlicensed spectrum

ABSTRACT

Methods and apparatuses are described in which an unlicensed spectrum is used for Long Term Evolution (LTE) communications. One method includes performing a clear channel assessment (CCA) for an unlicensed spectrum in a current gating interval to determine whether the unlicensed spectrum is available for a transmission in a next transmission interval, and gating OFF the transmission in the unlicensed spectrum for the next transmission interval when the determination is that the unlicensed spectrum is unavailable.

CROSS REFERENCES

The present application for patent claims priority to U.S. ProvisionalPatent Application No. 61/825,459 by Bhushan et al., entitled“LTE-Unlicensed,” filed May 20, 2013, assigned to the assignee hereof,and expressly incorporated by reference herein.

BACKGROUND

Wireless communication networks are widely deployed to provide variouscommunication services such as voice, video, packet data, messaging,broadcast, and the like. These wireless networks may be multiple-accessnetworks capable of supporting multiple users by sharing the availablenetwork resources.

A wireless communication network may include a number of base stationsor Node-Bs that can support communication for a number of userequipments (UEs). A UE may communicate with a base station via downlinkand uplink. The downlink (or forward link) refers to the communicationlink from the base station to the UE, and the uplink (or reverse link)refers to the communication link from the UE to the base station.

As wireless communications networks become more congested, operators arebeginning to look at ways to increase capacity. One approach may be touse Wireless Local Area Networks (WLANs) to offload some of the trafficand/or signaling. WLANs (or WiFi networks) are attractive because,unlike cellular networks that operate in a licensed spectrum, theygenerally operate in unlicensed spectrum. Moreover, a growing amountspectrum is being allocated for access without a license, making theoption of offloading traffic and/or signaling to WLANs more attractive.This approach, however, may provide a partial solution to the congestionproblem since WLANs tend to use spectrum less efficiently than cellularnetworks. Moreover, the regulations and protocols involved in WLANs aredifferent from those for cellular networks. Therefore, unlicensedspectrum may remain a reasonable option to alleviate congestion if itcan be used more efficiently and in accordance with regulatoryrequirements.

SUMMARY

Methods and apparatuses are described in which an unlicensed spectrummay be used for 3GPP Long Term Evolution (LTE) communications. Variousdeployment scenarios may be supported including a supplemental downlinkmode in which LTE downlink capacity in a licensed spectrum may beoffloaded to an unlicensed spectrum. A carrier aggregation mode may beused to offload both LTE downlink and uplink capacity from a licensedspectrum to an unlicensed spectrum. In a standalone mode, LTE downlinkand uplink communications between a base station (e.g., an evolved NodeB (eNB)) and a UE may take place in an unlicensed spectrum. Basestations as well as UEs may support one or more of these or similarmodes. Orthogonal Frequency-Division Multiple Access (OFDMA)communications signals may be used for LTE downlink communications in anunlicensed spectrum, while Single-Carrier Frequency-Division MultipleAccess (SC-FDMA) communications signals may be used for LTE uplinkcommunications in an unlicensed spectrum. The use of LTE configured foran unlicensed spectrum may be referred to as LTE-Unlicensed or LTE-U.

In a first set of illustrative examples, a method for wirelesscommunications is described. In one example, the method includesperforming a clear channel assessment (CCA) for an unlicensed spectrumin a current gating interval to determine whether the unlicensedspectrum is available for a transmission in a next transmissioninterval, and gating OFF the transmission in the unlicensed spectrum forthe next transmission interval when the determination is that theunlicensed spectrum is unavailable. In some embodiments, thetransmission includes a downlink transmission or an uplink transmission.In some embodiments, the method includes synchronizing the performanceof the CCA across a plurality of apparatuses. In some embodiments, theplurality of apparatuses includes a plurality of eNBs. In someembodiments, the method includes synchronizing the performance of theCCA across a plurality of eNBs from different operators. In someembodiments, the CCA is performed during a last subframe of the currentgating interval. In some embodiments, the CCA is performed during afirst subframe of the current gating interval.

In a second set of illustrative examples, an apparatus for wirelesscommunications is described. In one example, the apparatus includesmeans for performing CCA for an unlicensed spectrum in a current gatinginterval to determine whether the unlicensed spectrum is available for atransmission in a next transmission interval, and means for gating OFFthe transmission in the unlicensed spectrum for the next transmissioninterval when the determination is that the unlicensed spectrum isunavailable. In some embodiments, the transmission includes a downlinktransmission or an uplink transmission. In some embodiments, theapparatus includes means for synchronizing performance of the CCA acrossa plurality of apparatuses. In some embodiments, the plurality ofapparatuses includes a plurality of eNBs. In some embodiments, theapparatus includes means for synchronizing performance of the CCA acrossa plurality of eNBs from different operators. In some embodiments, theCCA is performed during a last subframe of the current gating interval.In some embodiments, the CCA is performed during a first subframe of thecurrent gating interval.

In a third set of illustrative examples, another apparatus for wirelesscommunications is described. In one example, the apparatus includes aprocessor, memory in electronic communication with the processor, andinstructions stored in the memory. The instructions may be executable bythe processor to perform CCA for an unlicensed spectrum in a currentgating interval to determine whether the unlicensed spectrum isavailable for a transmission in a next transmission interval, and gateOFF the transmission in the unlicensed spectrum for the nexttransmission interval when the determination is that the unlicensedspectrum is unavailable. In some embodiments, the transmission includesa downlink transmission or an uplink transmission. In some embodiments,the instructions are executable by the processor to synchronizeperformance of the CCA across a plurality of apparatuses. In someembodiments, the plurality of apparatuses includes a plurality of eNBs.In some embodiments, the instructions are executable by the processor tosynchronize performance of the CCA across a plurality of eNBs fromdifferent operators. In some embodiments, the CCA is performed during alast subframe of the current gating interval. In some embodiments, theCCA is performed during a first subframe of the current gating interval.

In a fourth set of illustrative examples, a computer program product forcommunications by a wireless communications apparatus in a wirelesscommunications system is described. In one example, the computer programproduct includes a non-transitory computer-readable medium storinginstructions executable by a processor to cause the wirelesscommunications apparatus to perform CCA for an unlicensed spectrum in acurrent gating interval to determine whether the unlicensed spectrum isavailable for a transmission in a next transmission interval, and gateOFF the transmission in the unlicensed spectrum for the nexttransmission interval when the determination is that the unlicensedspectrum is unavailable. In some embodiments, the transmission includesa downlink transmission or an uplink transmission. In some embodiments,the instructions are executable by the processor to cause the wirelesscommunications apparatus to synchronize performance of the CCA across aplurality of apparatuses. In some embodiments, the plurality ofapparatuses includes a plurality of eNBs. In some embodiments, theinstructions are executable by the processor to cause the wirelesscommunications apparatus to synchronize performance of the CCA across aplurality of eNBs from different operators. In some embodiments, the CCAis performed during a last subframe of the current gating interval. Insome embodiments, the CCA is performed during a first subframe of thecurrent gating interval.

The foregoing has outlined rather broadly the features and technicaladvantages of examples according to the disclosure in order that thedetailed description that follows may be better understood. Additionalfeatures and advantages will be described hereinafter. The conceptionand specific examples disclosed may be readily utilized as a basis formodifying or designing other structures for carrying out the samepurposes of the present disclosure. Such equivalent constructions do notdepart from the spirit and scope of the appended claims. Features whichare believed to be characteristic of the concepts disclosed herein, bothas to their organization and method of operation, together withassociated advantages will be better understood from the followingdescription when considered in connection with the accompanying figures.Each of the figures is provided for the purpose of illustration anddescription only, and not as a definition of the limits of the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

A further understanding of the nature and advantages of the presentdisclosure may be realized by reference to the following drawings. Inthe appended figures, similar components or features may have the samereference label. Further, various components of the same type may bedistinguished by following the reference label by a dash and a secondlabel that distinguishes among the similar components. If only the firstreference label is used in the specification, the description isapplicable to any one of the similar components having the same firstreference label irrespective of the second reference label.

FIG. 1 shows a diagram that illustrates an example of a wirelesscommunications system according to various embodiments;

FIG. 2A shows a diagram that illustrates examples of deploymentscenarios for using LTE in an unlicensed spectrum according to variousembodiments;

FIG. 2B shows a diagram that illustrates another example of a deploymentscenario for using LTE in an unlicensed spectrum according to variousembodiments;

FIG. 3 shows a diagram that illustrates an example of carrieraggregation when using LTE concurrently in licensed and unlicensedspectrum according to various embodiments;

FIG. 4A is a flowchart of an example of a method for concurrent use ofLTE in licensed and unlicensed spectrum in a base station according tovarious embodiments;

FIG. 4B is a flowchart of another example of a method for concurrent useof LTE in licensed and unlicensed spectrum in a base station accordingto various embodiments;

FIG. 5A is a flowchart of an example of a method for concurrent use ofLTE in licensed and unlicensed spectrum in a UE according to variousembodiments;

FIG. 5B is a flowchart of yet another example of a method for concurrentuse of LTE in licensed and unlicensed spectrum in a UE according tovarious embodiments;

FIG. 6A shows a diagram that illustrates an example of a periodic gatingstructure aligned to a periodic frame structure according to variousembodiments;

FIG. 6B shows a diagram that illustrates an example of a periodic gatingstructure that is half a periodic frame structure according to variousembodiments;

FIG. 6C shows a diagram that illustrates an example of a periodic gatingstructure that is twice a periodic frame structure according to variousembodiments;

FIG. 6D shows a diagram that illustrates an example of a periodic gatingstructure that is smaller than a periodic frame structure according tovarious embodiments;

FIG. 7A shows a diagram that illustrates an example of a periodic gatingstructure waveform according to various embodiments;

FIG. 7B shows a diagram that illustrates another example of a periodicgating structure waveform according to various embodiments;

FIG. 8 is a flowchart of an example of a method for synchronizing aperiodic gating structure with a periodic frame structure according tovarious embodiments;

FIG. 9A shows a diagram that illustrates an example of an S′ subframe ina periodic gating structure according to various embodiments;

FIG. 9B shows a diagram that illustrates an example of placement optionsfor clear channel assessment (CCA) slots in an S′ subframe according tovarious embodiments;

FIG. 9C shows a diagram that illustrates another example of an S′subframe in a periodic gating structure according to variousembodiments;

FIG. 9D shows a diagram that illustrates another example of an S′subframe in a periodic gating structure according to variousembodiments;

FIG. 10A shows a diagram that illustrates an example of gating when thechannel usage assessment occurs at the end of a previous gating intervalaccording to various embodiments;

FIG. 10B shows a diagram that illustrates an example of gating when thechannel usage assessment occurs at the beginning of a previous gatinginterval according to various embodiments;

FIG. 10C shows a diagram that illustrates an example of gating inresponse to WiFi transmission activity according to various embodiments;

FIG. 10D shows a diagram that illustrates an example of a periodicgating structure waveform with 14 Orthogonal Frequency-DivisionMultiplexing (OFDM) symbols according to various embodiments;

FIG. 10E shows a diagram that illustrates another example of a periodicgating structure waveform with 14 OFDM symbols according to variousembodiments;

FIG. 10F shows a diagram that illustrates an example of a periodicgating structure waveform with two subframes according to variousembodiments;

FIG. 10G shows a diagram that illustrates another example of a periodicgating structure waveform with two subframes according to variousembodiments;

FIG. 11 is a flowchart of an example of a method for gating a periodicstructure according to various embodiments;

FIG. 12A is a flowchart of an example of a method for synchronizing CAAslots across multiple base stations according to various embodiments;

FIG. 12B is a flowchart of another example of a method for synchronizingCAA slots across multiple base stations according to variousembodiments;

FIG. 13A is a flowchart of an example of a method for performing CAAwhen the CCA slots are synchronized across multiple base stationsaccording to various embodiments;

FIG. 13B is a flowchart of another example of a method for performingCAA when the CCA slots are synchronized across multiple base stationsaccording to various embodiments;

FIG. 14A shows a diagram that illustrates an example of the use ofChannel Usage Beacon Signals (CUBS) to reserve a channel in anunlicensed spectrum according to various embodiments;

FIG. 14B shows a diagram that illustrates another example of the use ofCUBS to reserve a channel in an unlicensed spectrum according to variousembodiments;

FIG. 14C shows a diagram that illustrates yet another example of the useof CUBS to reserve a channel in an unlicensed spectrum according tovarious embodiments;

FIG. 15 is a flowchart of an example of a method for transmittingsignals to reserve an unlicensed spectrum according to variousembodiments;

FIG. 16 shows a diagram that illustrates an example of feedbackinformation being sent in a licensed spectrum to address signalstransmitted in an unlicensed spectrum according to various embodiments;

FIG. 17A is a flowchart of an example of a method for receiving feedbackinformation via a Primary Component Carrier (PCC) uplink in a licensedspectrum according to various embodiments;

FIG. 17B is a flowchart of an example of a method for transmittingfeedback information via a PCC uplink in a licensed spectrum accordingto various embodiments;

FIG. 18A shows a diagram that illustrates an example of LTE-U beaconsignal broadcasting in an unlicensed spectrum according to variousembodiments;

FIG. 18B shows a diagram that illustrates an example of a payload in anLTE-U beacon signal according to various embodiments;

FIG. 19A is a flowchart of an example of a method for broadcasting LTE-Ubeacon signals in an unlicensed spectrum according to variousembodiments;

FIG. 19B is a flowchart of another example of a method for broadcastingLTE-U beacon signals in an unlicensed spectrum according to variousembodiments;

FIG. 20 shows a diagram that illustrates an example of request-to-send(RTS) and clear-to-send (CTS) signals in an unlicensed spectrumaccording to various embodiments;

FIG. 21 is a flowchart of an example of a method for transmitting RTSsignals and receiving CTS signals in an unlicensed spectrum according tovarious embodiments;

FIG. 22A shows a diagram that illustrates an example of virtual CTS(V-CTS) signals in a licensed spectrum according to various embodiments;

FIG. 22B shows a diagram that illustrates an example of a virtual RTS(V-RTS) signal and virtual V-CTS signals in a licensed spectrumaccording to various embodiments;

FIG. 23 is a flowchart of an example of a method for transmitting an RTSsignal or a V-RTS signal according to various embodiments;

FIG. 24 is a flowchart of an example of a method for receiving V-CTSsignals in response to an RTS signal or a V-RTS signal according tovarious embodiments;

FIG. 25 shows a diagram that illustrates an example of normal and robustsubframes in an unlicensed spectrum according to various embodiments;

FIG. 26 is a flowchart of an example of a method for transmitting normalor robust subframes in an unlicensed spectrum based on past transmissionactivity according to various embodiments;

FIG. 27 shows a diagram that illustrates an example of Physical UplinkControl Channel (PUCCH) signals and Physical Uplink Shared Channel(PUSCH) signals for an unlicensed spectrum according to variousembodiments;

FIG. 28 is a flowchart of an example of a method for generating PUCCHand/or PUSCH signals for an unlicensed spectrum according to variousembodiments;

FIG. 29 shows a diagram that illustrates an example of load-based gatingin an unlicensed spectrum according to various embodiments;

FIG. 30 shows a block diagram that illustrates an example of a UEarchitecture according to various embodiments;

FIG. 31 shows a block diagram that illustrates an example of a basestation architecture according to various embodiments; and

FIG. 32 shows a block diagram that illustrates an example of amultiple-input multiple-output (MIMO) communications system according tovarious embodiments.

DETAILED DESCRIPTION

Various systems, methods, and apparatuses are described in whichunlicensed spectrum is used for LTE communications. Various deploymentscenarios may be supported including a supplemental downlink mode inwhich LTE downlink traffic may be offloaded to an unlicensed spectrum. Acarrier aggregation mode may be used to offload both LTE downlink anduplink traffic from a licensed spectrum to an unlicensed spectrum. In astandalone mode, LTE downlink and uplink communications between a basestation (e.g., an eNB) and a UE may occur in an unlicensed spectrum. LTEand other base stations and UEs may support one or more of these orsimilar modes of operation. OFDMA communications signals may be used forLTE downlink communications in an unlicensed spectrum, while SC-FDMAcommunications signals may be used for LTE uplink communications in anunlicensed spectrum.

Operators have so far looked at WiFi as the primary mechanism to useunlicensed spectrum to relieve ever increasing levels of congestion incellular networks. However, a new carrier type (NCT) based on LTE in anunlicensed spectrum (LTE-U) may be compatible with carrier-grade WiFi,making LTE-U an alternative to WiFi. LTE-U may leverage LTE concepts andmay introduce some modifications to physical layer (PHY) and mediaaccess control (MAC) aspects of the network or network devices toprovide efficient operation in the unlicensed spectrum and to meetregulatory requirements. The unlicensed spectrum may range from 600Megahertz (MHz) to 6 Gigahertz (GHz), for example. In some scenarios,LTE-U may perform significantly better than WiFi. For example, in an allLTE-U deployment (for single or multiple operators), or when there aredense small cell LTE-U deployments, LTE-U may perform significantlybetter than WiFi. LTE-U may also perform better than WiFi in otherscenarios, such as when LTE-U is mixed with WiFi (for single or multipleoperators).

For a single service provider (SP), an LTE-U network on an unlicensedspectrum may be configured to be synchronous with an LTE network on alicensed spectrum. In some embodiments, some or all of the LTE-Unetworks deployed on a given channel by multiple SPs may also beconfigured to be synchronous across the multiple SPs. One approach toincorporate both the above features may involve using a constant timingoffset between LTE and LTE-U for a given SP. In some embodiments, someor all of the LTE-U networks deployed on a given channel by multiple SPsmay be configured to be asynchronous across the multiple SPs. An LTE-Unetwork may provide unicast and/or multicast services according to theneeds of the SP. Moreover, an LTE-U network may operate in abootstrapped mode in which LTE cells act as anchor and provide relevantLTE-U cell information (e.g., radio frame timing, common channelconfiguration, system frame number or SFN, etc.). In this mode, theremay be close interworking between LTE and LTE-U. For example, thebootstrapped mode may support the supplemental downlink and the carrieraggregation modes described above. The PHY-MAC layers of the LTE-Unetwork may operate in a standalone mode in which the LTE-U networkoperates independently from an LTE network. In this case, there may be aloose interworking between LTE and LTE-U based on RLC-level aggregationwith colocated LTE/LTE-U cells, or multiflow across multiple cellsand/or base stations, for example.

The techniques described herein are not limited to LTE, and may also beused for various wireless communications systems such as CDMA, TDMA,FDMA, OFDMA, SC-FDMA, and other systems. The terms “system” and“network” are often used interchangeably. A CDMA system may implement aradio technology such as CDMA2000, Universal Terrestrial Radio Access(UTRA), etc. CDMA2000 covers IS-2000, IS-95, and IS-856 standards.IS-2000 Releases 0 and A are commonly referred to as CDMA2000 1×, 1×,etc. IS-856 (TIA-856) is commonly referred to as CDMA2000 1×EV-DO, HighRate Packet Data (HRPD), etc. UTRA includes Wideband CDMA (WCDMA) andother variants of CDMA. A TDMA system may implement a radio technologysuch as Global System for Mobile Communications (GSM). An OFDMA systemmay implement a radio technology such as Ultra Mobile Broadband (UMB),Evolved UTRA (E-UTRA), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE802.20, Flash-OFDM, etc. UTRA and E-UTRA are part of Universal MobileTelecommunication System (UMTS). LTE and LTE-Advanced (LTE-A) are newreleases of UMTS that use E-UTRA. UTRA, E-UTRA, UMTS, LTE, LTE-A, andGSM are described in documents from an organization named “3rdGeneration Partnership Project” (3GPP). CDMA2000 and UMB are describedin documents from an organization named “3rd Generation PartnershipProject 2” (3GPP2). The techniques described herein may be used for thesystems and radio technologies mentioned above as well as other systemsand radio technologies. The description below, however, describes an LTEsystem for purposes of example, and LTE terminology is used in much ofthe description below, although the techniques are applicable beyond LTEapplications. In this description, LTE-Advanced (LTE-A) communicationsare considered to be a subset of LTE communications, and therefore,references to LTE communications encompass LTE-A communications.

The following description provides examples, and is not limiting of thescope, applicability, or configuration set forth in the claims. Changesmay be made in the function and arrangement of elements discussedwithout departing from the spirit and scope of the disclosure. Variousembodiments may omit, substitute, or add various procedures orcomponents as appropriate. For instance, the methods described may beperformed in an order different from that described, and various stepsmay be added, omitted, or combined. Also, features described withrespect to certain embodiments may be combined in other embodiments.

Referring first to FIG. 1, a diagram illustrates an example of awireless communications system or network 100. The system 100 includesbase stations (or cells) 105, communication devices 115, and a corenetwork 130. The base stations 105 may communicate with thecommunication devices 115 under the control of a base station controller(not shown), which may be part of the core network 130 or the basestations 105 in various embodiments. Base stations 105 may communicatecontrol information and/or user data with the core network 130 throughbackhaul links 132. In embodiments, the base stations 105 maycommunicate, either directly or indirectly, with each other overbackhaul links 134, which may be wired or wireless communication links.The system 100 may support operation on multiple carriers (waveformsignals of different frequencies). Multi-carrier transmitters cantransmit modulated signals simultaneously on the multiple carriers. Forexample, each communication link 125 may be a multi-carrier signalmodulated according to the various radio technologies described above.Each modulated signal may be sent on a different carrier and may carrycontrol information (e.g., reference signals, control channels, etc.),overhead information, data, etc.

The base stations 105 may wirelessly communicate with the devices 115via one or more base station antennas. Each of the base station 105sites may provide communication coverage for a respective geographicarea 110. In some embodiments, base stations 105 may be referred to as abase transceiver station, a radio base station, an access point, a radiotransceiver, a basic service set (BSS), an extended service set (ESS), aNodeB, eNodeB (eNB), Home NodeB, a Home eNodeB, or some other suitableterminology. The coverage area 110 for a base station may be dividedinto sectors making up only a portion of the coverage area (not shown).The system 100 may include base stations 105 of different types (e.g.,macro, micro, and/or pico base stations). There may be overlappingcoverage areas for different technologies.

In some embodiments, the system 100 may be an LTE/LTE-A network thatsupports one or more LTE-U modes of operation or deployment scenarios.In other embodiments, the system 100 may support wireless communicationsusing an unlicensed spectrum and an access technology different fromLTE-U, or a licensed spectrum and an access technology different fromLTE/LTE-A. The terms evolved Node B (eNB) and user equipment (UE) may begenerally used to describe the base stations 105 and devices 115,respectively. The system 100 may be a Heterogeneous LTE/LTE-A/LTE-Unetwork in which different types of eNBs provide coverage for variousgeographical regions. For example, each eNB 105 may providecommunication coverage for a macro cell, a pico cell, a femto cell,and/or other types of cell. Small cells such as pico cells, femto cells,and/or other types of cells may include low power nodes or LPNs. A macrocell generally covers a relatively large geographic area (e.g., severalkilometers in radius) and may allow unrestricted access by UEs withservice subscriptions with the network provider. A pico cell wouldgenerally cover a relatively smaller geographic area and may allowunrestricted access by UEs with service subscriptions with the networkprovider. A femto cell would also generally cover a relatively smallgeographic area (e.g., a home) and, in addition to unrestricted access,may also provide restricted access by UEs having an association with thefemto cell (e.g., UEs in a closed subscriber group (CSG), UEs for usersin the home, and the like). An eNB for a macro cell may be referred toas a macro eNB. An eNB for a pico cell may be referred to as a pico eNB.And, an eNB for a femto cell may be referred to as a femto eNB or a homeeNB. An eNB may support one or multiple (e.g., two, three, four, and thelike) cells.

The core network 130 may communicate with the eNBs 105 via a backhaul132 (e.g., 51, etc.). The eNBs 105 may also communicate with oneanother, e.g., directly or indirectly via backhaul links 134 (e.g., X2,etc.) and/or via backhaul links 132 (e.g., through core network 130).The system 100 may support synchronous or asynchronous operation. Forsynchronous operation, the eNBs may have similar frame and/or gatingtiming, and transmissions from different eNBs may be approximatelyaligned in time. For asynchronous operation, the eNBs may have differentframe and/or gating timing, and transmissions from different eNBs maynot be aligned in time. The techniques described herein may be used foreither synchronous or asynchronous operations.

The UEs 115 may be dispersed throughout the system 100, and each UE maybe stationary or mobile. A UE 115 may also be referred to by thoseskilled in the art as a mobile station, a subscriber station, a mobileunit, a subscriber unit, a wireless unit, a remote unit, a mobiledevice, a wireless device, a wireless communications device, a remotedevice, a mobile subscriber station, an access terminal, a mobileterminal, a wireless terminal, a remote terminal, a handset, a useragent, a mobile client, a client, or some other suitable terminology. AUE 115 may be a cellular phone, a personal digital assistant (PDA), awireless modem, a wireless communication device, a handheld device, atablet computer, a laptop computer, a cordless phone, a wireless localloop (WLL) station, or the like. A UE may be able to communicate withmacro eNBs, pico eNBs, femto eNBs, relays, and the like.

The communications links 125 shown in system 100 may include uplink (UL)transmissions from a mobile device 115 to a base station 105, and/ordownlink (DL) transmissions, from a base station 105 to a mobile device115. The downlink transmissions may also be called forward linktransmissions while the uplink transmissions may also be called reverselink transmissions. The downlink transmissions may be made using alicensed spectrum (e.g., LTE), an unlicensed spectrum (e.g., LTE-U), orboth (LTE/LTE-U). Similarly, the uplink transmissions may be made usinga licensed spectrum (e.g., LTE), an unlicensed spectrum (e.g., LTE-U),or both (LTE/LTE-U).

In some embodiments of the system 100, various deployment scenarios forLTE-U may be supported including a supplemental downlink mode in whichLTE downlink capacity in a licensed spectrum may be offloaded to anunlicensed spectrum, a carrier aggregation mode in which both LTEdownlink and uplink capacity may be offloaded from a licensed spectrumto an unlicensed spectrum, and a standalone mode in which LTE downlinkand uplink communications between a base station (e.g., eNB) and a UEmay take place in an unlicensed spectrum. Base stations 105 as well asUEs 115 may support one or more of these or similar modes of operation.OFDMA communications signals may be used in the communications links 125for LTE downlink transmissions in an unlicensed spectrum, while SC-FDMAcommunications signals may be used in the communications links 125 forLTE uplink transmissions in an unlicensed spectrum. Additional detailsregarding the implementation of LTE-U deployment scenarios or modes ofoperation in a system such as the system 100, as well as other featuresand functions related to the operation of LTE-U, are provided below withreference to FIGS. 2A-32.

Turning next to FIG. 2A, a diagram 200 shows examples of a supplementaldownlink mode and a carrier aggregation mode for an LTE network thatsupports LTE-U. The diagram 200 may be an example of portions of thesystem 100 of FIG. 1. Moreover, the base station 105-a may be an exampleof the base stations 105 of FIG. 1, while the UEs 115-a may be examplesof the UEs 115 of FIG. 1.

In the example of a supplemental downlink mode shown in diagram 200, thebase station 105-a may transmit OFDMA communications signals to a UE115-a using a downlink 205. The downlink 205 may be associated with afrequency F1 in an unlicensed spectrum. The base station 105-a maytransmit OFDMA communications signals to the same UE 115-a using abidirectional link 210 and may receive SC-FDMA communications signalsfrom that UE 115-a using the bidirectional link 210. The bidirectionallink 210 may be associated with a frequency F4 in a licensed spectrum.The downlink 205 in the unlicensed spectrum and the bidirectional link210 in the licensed spectrum may operate concurrently. The downlink 205may provide a downlink capacity offload for the base station 105-a. Insome embodiments, the downlink 205 may be used for unicast services(e.g., addressed to one UE) or multicast services (e.g., addressed toseveral UEs). This scenario may occur with any service provider (e.g., atraditional mobile network operator or MNO) that uses a licensedspectrum and needs to relieve some of the traffic and/or signalingcongestion in the licensed spectrum.

In one example of a carrier aggregation mode shown in diagram 200, thebase station 105-a may transmit OFDMA communications signals to a UE115-a using a bidirectional link 215 and may receive SC-FDMAcommunications signals from the same UE 115-a using the bidirectionallink 215. The bidirectional link 215 may be associated with thefrequency F1 in the unlicensed spectrum. The base station 105-a may alsotransmit OFDMA communications signals to the same UE 115-a using abidirectional link 220 and may receive SC-FDMA communications signalsfrom the same UE 115-a using the bidirectional link 220. Thebidirectional link 220 may be associated with a frequency F2 in alicensed spectrum. The bidirectional link 215 may provide a downlink anduplink capacity offload for the base station 105-a. Like thesupplemental downlink described above, this scenario may occur with anyservice provider (e.g., MNO) that uses a licensed spectrum and needs torelieve some of the traffic and/or signaling congestion.

In another example of a carrier aggregation mode shown in diagram 200,the base station 105-a may transmit OFDMA communications signals to a UE115-a using a bidirectional link 225 and may receive SC-FDMAcommunications signals from the same UE 115-a using the bidirectionallink 225. The bidirectional link 215 may be associated with thefrequency F3 in an unlicensed spectrum. The base station 105-a may alsotransmit OFDMA communications signals to the same UE 115-a using abidirectional link 230 and may receive SC-FDMA communications signalsfrom the same UE 115-a using the bidirectional link 230. Thebidirectional link 230 may be associated with the frequency F2 in thelicensed spectrum. The bidirectional link 225 may provide a downlink anduplink capacity offload for the base station 105-a. This example, andthose provided above, are presented for illustrative purposes and theremay be other similar modes of operation or deployment scenarios thatcombine LTE and LTE-U for capacity offload.

As described above, the typical service provider that may benefit fromthe capacity offload offered by using LTE-U (LTE in an unlicensedspectrum) is a traditional MNO with LTE licensed spectrum. For theseservice providers, an operational configuration may include abootstrapped mode (e.g., supplemental downlink, carrier aggregation)that uses the LTE primary component carrier (PCC) on the licensedspectrum and the LTE-U secondary component carrier (SCC) on theunlicensed spectrum.

In the supplemental downlink mode, control for LTE-U may be transportedover the LTE uplink (e.g., uplink portion of the bidirectional link210). One of the reasons to provide downlink capacity offload is becausedata demand is largely driven by downlink consumption. Moreover, in thismode, there may not be a regulatory impact since the UE is nottransmitting in the unlicensed spectrum. In some embodiments, there maybe no need to implement listen-before-talk (LBT) or carrier sensemultiple access (CSMA) requirements on the UE. However, LBT may beimplemented on the base station (e.g., eNB) by, for example, using aperiodic (e.g., every 10 milliseconds) clear channel assessment (CCA)and/or a grab-and-relinquish mechanism aligned to a radio frameboundary.

In the carrier aggregation mode, data and control may be communicated inLTE (e.g., bidirectional links 210, 220, and 230) while data may becommunicated in LTE-U (e.g., bidirectional links 215 and 225). Thecarrier aggregation mechanisms supported when using LTE-U may fall undera hybrid frequency division duplexing-time division duplexing (FDD-TDD)carrier aggregation or a TDD-TDD carrier aggregation with differentsymmetry across component carriers.

FIG. 2B shows a diagram 200-a that illustrates an example of astandalone mode for LTE-U. The diagram 200-a may be an example ofportions of the system 100 of FIG. 1. Moreover, the base station 105-bmay be an example of the base stations 105 of FIG. 1 and the basestation 105-a of FIG. 2A, while the UE 115-b may be an example of theUEs 115 of FIG. 1 and/or the UEs 115-a of FIG. 2A.

In the example of a standalone mode shown in diagram 200-a, the basestation 105-b may transmit OFDMA communications signals to the UE 115-busing a bidirectional link 240 and may receive SC-FDMA communicationssignals from the UE 115-b using the bidirectional link 240. Thebidirectional link 240 may be associated with the frequency F3 in anunlicensed spectrum described above with reference to FIG. 2A. Thestandalone mode may be used in non-traditional wireless accessscenarios, such as in-stadium access scenarios (e.g., unicast,multicast). The typical service provider for this mode of operation maybe a stadium owner, cable company, event host, hotel, enterprise, and/orlarge corporation that does not have licensed spectrum. For theseservice providers, an operational configuration for the standalone modemay use the LTE-U PCC on the unlicensed spectrum. Moreover, LBT may beimplemented on both the base station and the UE.

Turning next to FIG. 3, a diagram 300 illustrates an example of carrieraggregation when using LTE concurrently in licensed and unlicensedspectrum according to various embodiments. The carrier aggregationscheme in diagram 300 may correspond to the hybrid FDD-TDD carrieraggregation described above with reference to FIG. 2A. This type ofcarrier aggregation may be used in at least portions of the system 100of FIG. 1. Moreover, this type of carrier aggregation may be used in thebase stations 105 and 105-a of FIG. 1 and FIG. 2A, respectively, and/orin the UEs 115 and 115-a of FIG. 1 and FIG. 2A, respectively.

In this example, an FDD (FDD-LTE) may be performed in connection withLTE in the downlink, a first TDD (TDD1) may be performed in connectionwith LTE-U, a second TDD (TDD2) may be performed in connection with LTE,and another FDD (FDD-LTE) may be performed in connection with LTE in theuplink. TDD1 results in a DL:UL ratio of 6:4, while the ratio for TDD2is 7:3. On the time scale, the different effective DL:UL ratios are 3:1,1:3, 2:2, 3:1, 2:2, and 3:1. This example is presented for illustrativepurposes and there may be other carrier aggregation schemes that combinethe operations of LTE and LTE-U.

FIG. 4A shows a flowchart of a method 400 for concurrent use of LTE inlicensed and unlicensed spectrum by a first wireless node (e.g., a basestation or eNB) according to various embodiments. The method 400 may beimplemented using, for example, the base stations or eNBs 105, 105-a,and 105-b of FIG. 1, FIG. 2A, and FIG. 2B, respectively; and/or thesystem 100 of FIG. 1 and the portions of the system 200 and/or 200-a ofFIG. 2A and FIG. 2B. In one implementation, one of the base stations oreNBs 105 may execute one or more sets of codes to control the functionalelements of the base stations or eNB 105 to perform the functionsdescribed below.

At block 405, a first OFDMA communications signal may be transmitted toa second wireless node (e.g., UE 115) in a licensed spectrum. At block410, a second OFDMA communications signal may be transmitted to thesecond wireless node in an unlicensed spectrum concurrently with thetransmission of the first OFDMA communications signal. In someembodiments, the first and second OFDMA communications signals may betransmitted from at least one base station or eNB.

In some embodiments of the method 400, the transmission of the secondOFDMA communications signal in the unlicensed spectrum may betime-synchronized with the transmission of the first OFDMAcommunications signal in the licensed spectrum, with a fixed offsetbetween a frame structure of the first OFDMA communications signal and aframe structure of the second OFDMA communications signal. In someembodiments, the fixed offset may be zero or substantially zero.

In some embodiments of the method 400, a first SC-FDMA communicationssignal may be may be received from the second wireless node in alicensed spectrum concurrently with the transmission of the first andsecond OFDMA communication signals. The first SC-FDMA communicationssignal received from the second wireless node in the licensed spectrummay carry signaling or other control information related to the secondOFDMA communications signal transmitted in the unlicensed spectrum. Themethod may include receiving, concurrently with the transmission of thefirst and second OFDMA communications signals, a second SC-FDMAcommunications signal from the second wireless node in an unlicensedspectrum. The method may include receiving, concurrently with thetransmission of the first and second OFDMA communications signals, afirst SC-FDMA communications signal from the in a licensed spectrum anda second SC-FDMA communications signal from the UE in an unlicensedspectrum. In some embodiments, each of the first and second OFDMAcommunications signals may include an LTE signal.

FIG. 4B shows a flowchart of a method 400-a for concurrent use of LTE inlicensed and unlicensed spectrum by a first wireless node (e.g., a basestation or eNB) according to various embodiments. The method 400-a, likethe method 400 above, may be implemented using, for example, the basestations or eNBs 105, 105-a, and 105-b of FIG. 1, FIG. 2A, and FIG. 2B,respectively; and/or the system 100 of FIG. 1 and the portions of thesystem 200 and/or 200-a of FIG. 2A and FIG. 2B. In one implementation,one of the base stations or eNBs 105 may execute one or more sets ofcodes to control the functional elements of the base station or eNB 105to perform the functions described below.

At block 415, a first SC-FDMA communications signal may be received froma second wireless node (e.g., UE 115) in a licensed spectrum.

At block 420, a second SC-FDMA communications signal may be receivedfrom the second wireless node in an unlicensed spectrum concurrentlywith the reception of the first OFDMA communications signal. In someembodiments, the first and second SC-FDMA communications signals may bereceived from at least one UE. In some embodiments, each of the firstand second SC-FDMA communications signals may include an LTE signal.

FIG. 5A shows a flowchart of a method 500 for concurrent use of LTE inlicensed and unlicensed spectrum by a first wireless node (e.g., a UE)according to various embodiments. The method 500 may be implementedusing, for example, the UEs 115, 115-a, and 115-b of FIG. 1, FIG. 2A,and FIG. 2B, respectively; and/or the system 100 of FIG. 1 and theportions of the system 200 and/or 200-a of FIG. 2A and FIG. 2B. In oneimplementation, one of the UEs 115 may execute one or more sets of codesto control the functional elements of the UE 115 to perform thefunctions described below.

At block 505, a first OFDMA communications signal may be received from asecond wireless node (e.g., a base station or eNB 105) in a licensedspectrum.

At block 510, a second OFDMA communications signal may be received fromthe second wireless node in an unlicensed spectrum concurrently with thereception of the first OFDMA communications signal. In some embodiments,the first and second OFDMA communications signals may be received at aUE.

In some embodiments of the method 500, a first SC-FDMA communicationssignal may be transmitted to the second wireless node in a licensedspectrum concurrently with the reception of the first and second OFDMAcommunications signals. The first SC-FDMA communications signal receivedtransmitted to the second wireless node in the licensed spectrum maycarry signaling or other control information related to the second OFDMAsignal received on the unlicensed spectrum. The method may includetransmitting, concurrently with the reception of the first and secondOFDMA communications signals, a second SC-FDMA communications signal tothe second wireless node in an unlicensed spectrum. The method mayinclude transmitting, concurrently with the reception of the first andsecond OFDMA communications signals, a first SC-FDMA communicationssignal to the second wireless node in a licensed spectrum and a secondSC-FDMA communications signal to the second wireless node in anunlicensed spectrum. Each of the first and second OFDMA communicationssignals may include an LTE signal.

FIG. 5B shows a flowchart of a method 500-a for concurrent use of LTE inlicensed and unlicensed spectrum by a first wireless node (e.g., a UE)according to various embodiments. The method 500-a, like the method 500above, may be implemented using, for example, the UEs 115, 115-a, and115-b of FIG. 1, FIG. 2A, and FIG. 2B, respectively; and/or the system100 of FIG. 1 and the portions of the system 200 and/or 200-a of FIG. 2Aand FIG. 2B. In one implementation, one of the UEs 115 may execute oneor more sets of codes to control the functional elements of the UE 115to perform the functions described below.

At block 515, a first SC-FDMA communications signal may be transmittedto a second wirelessnode (e.g., a base station or eNB 105) in a licensedspectrum.

At block 520, a second SC-FDMA communications signal may be transmittedto the second wireless node in an unlicensed spectrum concurrently withthe transmission of the first SC-FDMA communications signal. In someembodiments, the first and second SC-FDMA communications signals may betransmitted from a UE. In some embodiments, each of the first and secondSC-FDMA communications signals may include an LTE signal.

In some embodiments, a transmitting device such as a base station, eNB105, UE 115 (or a transmitter of a transmitting device) may use a gatinginterval to gain access to a channel of the unlicensed spectrum. Thegating interval may define the application of a contention-basedprotocol, such as a Listen Before Talk (LBT) protocol based on the LBTprotocol specified in ETSI (EN 301 893). When using a gating intervalthat defines the application of an LBT protocol, the gating interval mayindicate when a transmitting device needs to perform a Clear ChannelAssessment (CCA). The outcome of the CCA indicates to the transmittingdevice whether a channel of the unlicensed spectrum is available or inuse. When the CCA indicates that the channel is available (e.g., “clear”for use), the gating interval may allow the transmitting device to usethe channel—typically for a predefined period of time. When the CCAindicates that the channel is not available (e.g., in use or reserved),the gating interval may prevent the transmitting device from using thechannel for a period of time.

In some cases, it may be useful for a transmitting device to generate agating interval on a periodic basis and synchronize at least oneboundary of the gating interval with at least one boundary of a periodicframe structure. For example, it may be useful to generate a periodicgating interval for a downlink in an unlicensed spectrum, and tosynchronize at least one boundary of the periodic gating interval withat least one boundary of a periodic frame structure associated with thedownlink Examples of such synchronization are illustrated in FIGS. 6A,6B, 6C, and 6D.

FIG. 6A illustrates a first example 600 of a periodic gating interval605 for transmissions (uplink and/or downlink) in an unlicensedspectrum. The periodic gating interval 605 may be used by an eNB thatsupports LTE-U (LTE-U eNB). Examples of such an eNB may be the basestations 105, 105-a, and 105-b of FIG. 1, FIG. 2A, and FIG. 2B,respectively. The gating interval 605 may be used with the system 100 ofFIG. 1 and with portions of the system 200 and/or 200-a shown in FIG. 2Aand FIG. 2B.

By way of example, the duration of the periodic gating interval 605 isshown to be equal to (or approximately equal to) the duration of theperiodic frame structure 610. In some embodiments, the periodic framestructure 610 may be associated with a primary component carrier (PCC)of a downlink. In some embodiments, “approximately equal” means theduration of the periodic gating interval 605 is within a cyclic prefix(CP) duration of the duration of the periodic frame structure 610.

At least one boundary of the periodic gating interval 605 may besynchronized with at least one boundary of the periodic frame structure610. In some cases, the periodic gating interval 605 may have boundariesthat are aligned with the frame boundaries of the periodic framestructure 610. In other cases, the periodic gating interval 605 may haveboundaries that are synchronized with, but offset from, the frameboundaries of the periodic frame structure 610. For example, theboundaries of the periodic gating interval 605 may be aligned withsubframe boundaries of the periodic frame structure 610, or withsubframe midpoint boundaries (e.g., the midpoints of particularsubframes) of the periodic frame structure 610.

In some cases, each periodic frame structure 610 may include an LTEradio frame (e.g., an LTE radio frame (N−1), an LTE radio frame (N), oran LTE radio frame (N+1)). Each LTE radio frame may have a duration often milliseconds, and the periodic gating interval 605 may also have aduration of ten milliseconds. In these cases, the boundaries of theperiodic gating interval 605 may be synchronized with the boundaries(e.g., frame boundaries, subframe boundaries, or subframe midpointboundaries) of one of the LTE radio frames (e.g., the LTE radio frame(N)).

FIG. 6B illustrates a second example 600-a of a periodic gating interval605-a for transmissions (uplink and/or downlink) in an unlicensedspectrum. The periodic gating interval 605-a may be used by an eNB thatsupports LTE-U (LTE-U eNB). Examples of such an eNB may be the basestations 105, 105-a, and 105-b of FIG. 1, FIG. 2A, and FIG. 2B,respectively. The gating interval 605 may be used with the system 100 ofFIG. 1 and with portions of the system 200 and/or 200-a shown in FIG. 2Aand FIG. 2B.

By way of example, the duration of the periodic gating interval 605-a isshown to be a sub-multiple of (or an approximate sub-multiple of) theduration of the periodic frame structure 610. In some embodiments, an“approximate sub-multiple of” means the duration of the periodic gatinginterval 605-a is within a cyclic prefix (CP) duration of the durationof a sub-multiple of (e.g., half) the periodic frame structure 610.

At least one boundary of the periodic gating interval 605-a may besynchronized with at least one boundary of the periodic frame structure610. In some cases, the periodic gating interval 605-a may have aleading or trailing boundary that is aligned with a leading or trailingframe boundary of the periodic frame structure 610. In other cases, theperiodic gating interval 605-a may have boundaries that are synchronizedwith, but offset from, each of the frame boundaries of the periodicframe structure 610. For example, the boundaries of the periodic gatinginterval 605-a may be aligned with subframe boundaries of the periodicframe structure 610, or with subframe midpoint boundaries (e.g., themidpoints of particular subframes) of the periodic frame structure 610.

In some cases, each periodic frame structure 610 may include an LTEradio frame (e.g., an LTE radio frame (N−1), an LTE radio frame (N), oran LTE radio frame (N+1)). Each LTE radio frame may have a duration often milliseconds, and the periodic gating interval 605-a may have aduration of five milliseconds. In these cases, the boundaries of theperiodic gating interval 605-a may be synchronized with the boundaries(e.g., frame boundaries, subframe boundaries, or subframe midpointboundaries) of one of the LTE radio frames (e.g., LTE radio frame (N)).The periodic gating interval 605-a may then be repeated, for example,every periodic frame structure 610, more than once every periodic framestructure 610 (e.g., twice), or once every Nth periodic frame structure610 (e.g., for N=2, 3, . . . ).

FIG. 6C illustrates a third example 600-b of a periodic gating interval605-b for transmissions (uplink and/or downlink) in an unlicensedspectrum. The periodic gating interval 605-b may be used by an eNB thatsupports LTE-U (LTE-U eNB). Examples of such an eNB may be the basestations 105, 105-a, and 105-b of FIG. 1, FIG. 2A, and FIG. 2B,respectively. The gating interval 605 may be used with the system 100 ofFIG. 1 and with portions of the system 200 and/or 200-a shown in FIG. 2Aand FIG. 2B.

By way of example, the duration of the periodic gating interval 605-b isshown to be an integer multiple of (or an approximate integer multipleof) the duration of the periodic frame structure 610. In someembodiments, an “approximate integer multiple of” means the duration ofthe periodic gating interval 605-b is within a cyclic prefix (CP)duration of an integer multiple of (e.g., double) the duration of theperiodic frame structure 610.

At least one boundary of the periodic gating interval 605-b may besynchronized with at least one boundary of the periodic frame structure610. In some cases, the periodic gating interval 605-b may have aleading boundary and a trailing boundary that are aligned withrespective leading or trailing frame boundaries of the periodic framestructure 610. In other cases, the periodic gating interval 605-b mayhave boundaries that are synchronized with, but offset from, the frameboundaries of the periodic frame structure 610. For example, theboundaries of the periodic gating interval 605-b may be aligned withsubframe boundaries of the periodic frame structure 610, or withsubframe midpoint boundaries (e.g., the midpoints of particularsubframes) of the periodic frame structure 610.

In some cases, each periodic frame structure 610 may include an LTEradio frame (e.g., an LTE radio frame (N−1), an LTE radio frame (N), oran LTE radio frame (N+1)). Each LTE radio frame may have a duration often milliseconds, and the periodic gating interval 605-b may have aduration of twenty milliseconds. In these cases, the boundaries of theperiodic gating interval 605-b may be synchronized with the boundaries(e.g., frame boundaries, subframe boundaries, or subframe midpointboundaries) of one or two of the LTE radio frames (e.g., LTE radio frame(N) and LTE radio frame (N+1)).

FIG. 6D illustrates a fourth example 600-c of a periodic gating interval605-c for transmissions (uplink and/or downlink) in an unlicensedspectrum. The periodic gating interval 605-c may be used by an eNB thatsupports LTE-U (LTE-U eNB). Examples of such an eNB may be the basestations 105, 105-a, and 105-b of FIG. 1, FIG. 2A, and FIG. 2B,respectively. The gating interval 605 may be used with the system 100 ofFIG. 1 and with portions of the system 200 and/or 200-a shown in FIG. 2Aand FIG. 2B.

By way of example, the duration of the periodic gating interval 605-c isshown to be a sub-multiple of (or an approximate sub-multiple of) theduration of the periodic frame structure 610. The sub-multiple may beone-tenth of the duration of the periodic frame structure 610.

At least one boundary of the periodic gating interval 605-c may besynchronized with at least one boundary of the periodic frame structure610. In some cases, the periodic gating interval 605-c may have aleading or trailing boundary that is aligned with a leading or trailingframe boundary of the periodic frame structure 610. In other cases, theperiodic gating interval 605-c may have boundaries that are synchronizedwith, but offset from, each of the frame boundaries of the periodicframe structure 610. For example, the boundaries of the periodic gatinginterval 605-c may be aligned with subframe boundaries of the periodicframe structure 610, or with subframe midpoint boundaries (e.g., themidpoints of particular subframes) of the periodic frame structure 610.

In some cases, each periodic frame structure 610 may include an LTEradio frame (e.g., an LTE radio frame (N−1), an LTE radio frame (N), oran LTE radio frame (N+1)). Each LTE radio frame may have a duration often milliseconds, and the periodic gating interval 605-c may have aduration of one millisecond (e.g., the duration of one subframe). Inthese cases, the boundaries of the periodic gating interval 605-c may besynchronized with the boundaries (e.g., frame boundaries, subframeboundaries, or subframe midpoint boundaries) of one of the LTE radioframes (e.g., LTE radio frame (N)). The periodic gating interval 605-cmay then be repeated, for example, every periodic frame structure 610,more than once every periodic frame structure 610, or once every Nthperiodic frame structure 610 (e.g., for N=2, 3, . . . ).

FIG. 7A illustrates a fifth example 700 of a periodic gating interval605-d-1 for transmissions (uplink and/or downlink) in an unlicensedspectrum. The periodic gating interval 605-d-1 may be used by an eNBthat supports LTE-U (LTE-U eNB). Examples of such an eNB may be the basestations 105, 105-a, and 105-b of FIG. 1, FIG. 2A, and FIG. 2B,respectively. The gating interval 605-d-1 may be used with the system100 of FIG. 1 and with portions of the system 200 and/or 200-a shown inFIG. 2A and FIG. 2B.

By way of example, the duration of the periodic gating interval 605-d-1is shown to be equal to (or approximately equal to) the duration of aperiodic frame structure 610-a. In some embodiments, the periodic framestructure 610-a may be associated with a primary component carrier (PCC)of a downlink. The boundaries of the periodic gating interval 605-d-1may be synchronized with (e.g., aligned with) the boundaries of theperiodic frame structure 610-a.

The periodic frame structure 610-a may include an LTE radio frame havingten subframes (e.g., SF0, SF1, SF9). Subframes SF0 through SF8 may bedownlink (D) subframes 710, and subframe SF9 may be a special (S′)subframe 715. The D and/or S′ subframes 710 and/or 715 may collectivelydefine a channel occupancy time of the LTE radio frame, and at leastpart of the S′ subframe 715 may define a channel idle time. Under thecurrent LTE standard, an LTE radio frame may have a maximum channeloccupancy time (ON time) between one and 9.5 milliseconds, and a minimumchannel idle time (OFF time) of five percent of the channel occupancytime (e.g., a minimum of 50 microseconds). To ensure compliance with theLTE standard, the periodic gating interval 605-d may abide by theserequirements of the LTE standard by providing a 0.5 millisecond guardperiod (i.e., OFF time) as part of the S′ subframe 715.

Because the S′ subframe 715 has a duration of one millisecond, it mayinclude one or more CCA slots 720 (e.g., time slots) in which thetransmitting devices contending for a particular channel of anunlicensed spectrum may perform their CCAs. When a transmitting device'sCCA indicates the channel is available, but the device's CCA iscompleted before the end of the periodic gating interval 605-d-1, thedevice may transmit one or more signals to reserve the channel until theend of the periodic gating interval 605-d-1. The one or more signals mayin some cases include Channel Usage Pilot Signals (CUPS) or ChannelUsage Beacon Signals (CUBS) 730. CUBS 730 are described in detail laterin this description, but may be used for both channel synchronizationand channel reservation. That is, a device that performs a CCA for thechannel after another device begins to transmit CUBS on the channel maydetect the energy of the CUBS 730 and determine that the channel iscurrently unavailable.

Following a transmitting device's successful completion of a CCA for achannel and/or the transmission of CUBS 730 over a channel, thetransmitting device may use the channel for up to a predetermined periodof time (e.g., one gating interval or one LTE radio frame) to transmit awaveform (e.g., an LTE-based waveform 740).

FIG. 7B illustrates a sixth example 705 of a periodic gating interval605-d-2 for transmissions (uplink and/or downlink) in an unlicensedspectrum. The periodic gating interval 605-d-2 may be used by an eNB orUE that supports LTE-U (LTE-U eNB or LTE-U UE). Examples of such an eNBmay be the base stations 105, 105-a, and 105-b of FIG. 1, FIG. 2A, andFIG. 2B, respectively, and examples of such a UE may be the UEs 115,115-a, and 115-b of FIG. 1. The gating interval 605-d-2 may be used withthe system 100 of FIG. 1 and with portions of the system 200 and/or200-a shown in FIG. 2A and FIG. 2B.

By way of example, the duration of the periodic gating interval 605-d-2is shown to be equal to (or approximately equal to) the duration of aperiodic frame structure 610-a. In some embodiments, the periodic framestructure 610-a may be associated with a primary component carrier (PCC)of a downlink. The boundaries of the periodic gating interval 605-d-2may be synchronized with (e.g., aligned with) the boundaries of theperiodic frame structure 610-a.

The periodic frame structure 610-b may include an LTE radio frame havingten subframes (e.g., SF0, SF1, SF9). Subframes SF0 through SF4 may bedownlink (D) subframes 710; subframe SF5 may be a special (S) subframe735; subframes SF6 through SF8 may be uplink (U) subframes 745; andsubframe SF9 may be a special (S′) subframe 715. The D, S, U, and/or S′subframes 710, 735, 745, and/or 715 may collectively define a channeloccupancy time of the LTE radio frame, and at least part of the Ssubframe 735 and/or S′ subframe 715 may define a channel idle time.Under the current LTE standard, an LTE radio frame may have a maximumchannel occupancy time (ON time) between one and 9.5 milliseconds, and aminimum channel idle time (OFF time) of five percent of the channeloccupancy time (e.g., a minimum of 50 microseconds). To ensurecompliance with the LTE standard, the periodic gating interval 605-d-2may abide by these requirements of the LTE standard by providing a 0.5millisecond guard period or silence period (i.e., OFF time) as part ofthe S subframe 735 and/or S′ subframe 715.

Because the S′ subframe 715 has a duration of one millisecond, it mayinclude one or more CCA slots 720 (e.g., time slots) in which thetransmitting devices contending for a particular channel of anunlicensed spectrum may perform their CCAs. When a transmitting device'sCCA indicates the channel is available, but the device's CCA iscompleted before the end of the periodic gating interval 605-d-2, thedevice may transmit one or more signals to reserve the channel until theend of the periodic gating interval 605-d-2. The one or more signals mayin some cases include CUPS or CUBS 730. CUBS 730 are described in detaillater in this description, but may be used for both channelsynchronization and channel reservation. That is, a device that performsa CCA for the channel after another device begins to transmit CUBS onthe channel may detect the energy of the CUBS 730 and determine that thechannel is currently unavailable.

Following a transmitting device's successful completion of a CCA for achannel and/or the transmission of CUBS 730 over a channel, thetransmitting device may use the channel for up to a predetermined periodof time (e.g., one gating interval or one LTE radio frame) to transmit awaveform (e.g., an LTE-based waveform 740).

When a channel of the unlicensed spectrum is reserved, for example, by abase station or eNB for a gating interval or LTE radio frame, the basestation or eNB may in some cases reserve the channel for Time DomainMultiplexing (TDM) use. In these examples, the base station or eNB maytransmit data in a number of D subframes (e.g., subframes SF0 throughSF4) and then allow a UE with which it is communicating to perform a CCA750 (e.g., an uplink CCA) in an S subframe (e.g., subframe SF5). Whenthe CCA 750 is successful, the UE may transmit data to the base stationor eNB in a number of U subframes (e.g., subframes SF6 through SF8).

When a gating interval defines an application of the LBT protocolspecified in ETSI (EN 301 893), the gating interval may take the form ofan LBT Fixed Based Equipment (LBT-FBE) gating interval or an LBT LoadBased Equipment (LBT-LBE) gating interval. An LBT-FBE gating intervalmay have a fixed/periodic timing and may not be directly influenced bytraffic demand (e.g., its timing can be changed throughreconfiguration). In contrast, an LBT-LBE gating interval may not have afixed timing (i.e., be asynchronous) and may be largely influenced bytraffic demand. FIGS. 6A, 6B, 6C, 6D, and 7 each illustrate an exampleof a periodic gating interval 605, which periodic gating interval 605may be an LBT-FBE gating interval. A potential advantage of the periodicgating interval 605 described with reference to FIG. 6A is that it maypreserve the ten millisecond LTE radio frame structure defined in thecurrent LTE specification. However, when the duration of a gatinginterval is less than the duration of an LTE radio frame (e.g., asdescried with reference to FIG. 6B or 6D), the advantages of preservingthe LTE radio frame structure no longer exist and an LBT-LBE gatinginterval may be advantageous. A potential advantage of using an LBT-LBEgating interval is that it may retain the subframe structure of LTE PHYchannels, without any symbol puncturing at the beginning or end of thegating interval. However, a potential disadvantage of using an LBT-LBEgating interval is not being able to synchronize the use of a gatinginterval between the different eNBs of an LTE-U operator (e.g., becauseeach eNB uses a random back-off time for an extended CCA).

FIG. 8 is a flow chart illustrating an example of a method 800 forwireless communications. For clarity, the method 800 is described belowwith reference to one of the eNBs 105 or UEs 115 shown in FIGS. 1, 2A,and/or 2B. In one implementation, one of the eNBs 105 or UEs 115 mayexecute one or more sets of codes to control the functional elements ofthe eNB 105 or UE 115 to perform the functions described below.

At block 805, a periodic gating interval for a downlink in an unlicensedspectrum may be generated.

At block 810, at least one boundary of the periodic gating interval maybe synchronized with at least one boundary of a periodic frame structureassociated with a PCC of the downlink. In some embodiments, the PCC mayinclude a carrier in a licensed spectrum.

In some embodiments, the periodic gating interval may include an LBTframe and/or the periodic frame structure may include an LTE radioframe.

In some embodiments, the duration of the periodic gating interval may bean integer multiple of the duration of the periodic frame structure.Examples of such an embodiment are described, supra, with reference toFIGS. 6A and 6C. In other embodiments, the duration of the periodicgating interval may be a sub-multiple of the duration of the periodicframe structure. Examples of such an embodiment are described, supra,with reference to FIGS. 6B and 6D.

Thus, the method 800 may provide for wireless communications. It shouldbe noted that the method 800 is just one implementation and that theoperations of the method 800 may be rearranged or otherwise modifiedsuch that other implementations are possible.

FIGS. 9A, 9B, 9C, and 9D illustrate examples 900, 900-a, 920, 950 of howa contention-based protocol such as LBT may be implemented within an S′subframe 725-a of a gating interval, such as an S′ subframe of the tenmillisecond gating interval 605-d-1 or 605-d-2 described with referenceto FIG. 7A or 7B. The contention-based protocol may be used with, forexample, the base stations 105, 105-a, and 105-b of FIG. 1, FIG. 2A, andFIG. 2B, respectively. The contention-based protocol may be used withthe system 100 of FIG. 1 and with portions of the system 200 and/or200-a shown in FIG. 2A and FIG. 2B.

Referring now to FIGS. 9A and 9B, there is shown an example 900/900-a ofan S′ subframe 725-a-1 having a guard period 905 and a CCA period 910.By way of example, each of the guard period 905 and the CCA period 910may have a duration of 0.5 milliseconds and include seven OFDM symbolpositions 915. As shown in FIG. 9B, each of the OFDM symbol positions915 in the CCA period 910 may be transformed into a CCA slot 720-a uponan eNB selecting the OFDM symbol position 915 for performing CCA. Insome cases, the same or different ones of the OFDM symbol positions 915may be pseudo-randomly selected by ones of multiple eNBs, therebyproviding a sort of CCA time dithering. The eNBs may be operated by asingle LTE-U operator or different LTE-U operators. An OFDM symbolposition 915 may be pseudo-randomly selected in that an eNB may beconfigured to select different ones of the OFDM symbol positions atdifferent times, thereby giving each of the multiple eNBs an opportunityto select the OFDM symbol position 915 that occurs earliest in time.This may be advantageous in that the first eNB to perform a successfulCCA has an opportunity to reserve a corresponding channel or channels ofan unlicensed spectrum, and an eNB's pseudo-random selection of an OFDMsymbol position 915 for performing CCA ensures that it has the samechance of performing a successful CCA as every other eNB. In the case ofeNBs operated by a single LTE-U operator, the eNBs may in some cases beconfigured to select the same CCA slot 720-a.

FIG. 9C shows an example 920 of an S′ subframe 725-a-2 having a guardperiod 905 and a CCA period 910. By way of example, each the guardperiod 905 may have a duration of 0.5 milliseconds and include sevenOFDM symbol positions. The CCA period 910 may include one OFDM symbolposition or a fraction of one OFDM symbol position, which may includeone or more CCA slots, each having a duration less than or equal to anOFDM symbol position. The CCA period 910 may be followed by a CUBSperiod 930. The guard period 905 may be preceded by a shortened Dsubframe 925. In some examples, all of the wireless nodes (e.g., allbase stations or eNBs) associated with an operator or public land mobilenetwork (PLMN) may perform a CCA at the same time during the CCA period910. The S′ subframe 725-a-2 shown in FIG. 9C may be useful in scenarioswhere an operator operates asynchronously with respect to otheroperators with which it competes for access to an unlicensed spectrum.

FIG. 9D shows an example 950 of an S′ subframe 725-a-3 having ashortened D subframe 925, a CCA period 910, and a CUBS period 930. TheCCA period 910 may include one OFDM symbol position or a fraction of oneOFDM symbol position, which may include one or more CCA slots, eachhaving a duration less than or equal to an OFDM symbol position. The CCAperiod 910 may be followed by a CUBS period 930. In some examples, allof the wireless nodes (e.g., all base stations or eNBs) associated withan operator or public land mobile network (PLMN) may perform a CCA atthe same time during the CCA period 910. The S′ subframe 725-a-3 shownin FIG. 9D may be useful in scenarios where an operator operatesasynchronously with respect to other operators with which it competesfor access to an unlicensed spectrum, and where the S′ subframe 725-a-3is used in a TDM context, such as with the gating interval 605-d-2. Whenused in a TDM context, a silent period may provided in an S subframe ofa frame of which the S′ subframe 725-a-3 forms a part.

FIGS. 10A and 10B provide examples of how an S′ subframe such as the S′subframe 725-a described with reference to FIGS. 9A and/or 9B may beused in conjunction with a current gating interval 605. By way ofexample, the current gating intervals 605-e, 605-g shown in FIGS. 10Aand 10B may be examples of the ten millisecond gating interval 605-ddescribed with reference to FIG. 7. The use of S′ subframes inconjunction with a current gating interval may be handled by, forexample, the base stations 105, 105-a, and 105-b of FIG. 1, FIG. 2A, andFIG. 2B, respectively. The use of S′ subframes in conjunction with acurrent gating interval may be handled may be the system 100 of FIG. 1and with portions of the system 200 and/or 200-a shown in FIG. 2A and/orFIG. 2B.

FIG. 10A provides an example 1000 in which an S′ subframe is included asa last subframe of the current gating interval 605-e. Thus, the guardperiod 905-a and the CCA period 910-a of the S′ subframe occur at theend of the current gating interval 605-e, just prior to a trailingboundary of the current gating interval 605-e and the start of a nexttransmission interval 605-f. The next transmission interval 605-f may begated ON or gated OFF for a downlink transmission of each of a number oftransmitting devices, depending on whether a CCA performed by thetransmitting device indicates that unlicensed spectrum is available orunavailable during the next transmission interval 605-f. In some cases,the next transmission interval 605-f may also be a next gating interval.

FIG. 10B provides an example 1000-a in which an S′ subframe is includedas a first subframe of the current gating interval 605-g. Thus, theguard period 905-b and the CCA period 910-b of the S′ subframe occur atthe start of the current gating interval 605-g, just after a leadingboundary of the current gating interval 605-g. The next transmissioninterval 605-h may be gated ON or gated OFF for a downlink transmissionof each of a number of transmitting devices, depending on whether a CCAperformed by the transmitting device indicates that unlicensed spectrumis available or unavailable during the next transmission interval 605-f.In some cases, the next transmission interval 605-h may also be a nextgating interval.

FIG. 10C provides an example 1000-b of how the performance of CCAs foran unlicensed spectrum (or a channel of the unlicensed spectrum) may besynchronized across multiple eNBs 105. By way of example, the multipleeNBs 105 may include an LTE-U eNB1 and an LTE-U eNB2. The performance ofCCAs may be provided by, for example, the base stations 105, 105-a, and105-b of FIG. 1, FIG. 2A, and FIG. 2B, respectively. The performance ofCCAs may used in the system 100 of FIG. 1 and with portions of thesystem 200 and/or 200-a shown in FIG. 2A and/or FIG. 2B.

Because of synchronization between the eNB1 and the eNB2, an S′ subframe725-b within a current gating interval of the eNB1 may be synchronizedwith an S′ subframe 725-c within a current gating interval of the eNB2.Also, and because of a synchronized pseudo-random CCA slot selectionprocesses implemented by each eNB, the eNB2 may select a CCA slot 720-cthat occurs at a different time (e.g., different OFDM symbol position)than the CCA slot 720-b selected by eNB1. For example, the eNB1 mayselect a CCA slot 720-b aligned with the fifth OFDM symbol position ofthe aligned CCA periods of the S′ subframes 725-b and 725-c, and theeNB2 may select a CCA slot 720-c aligned with the third OFDM symbolposition of the aligned CCA periods.

A next transmission interval following the synchronized S′ subframes725-b and 725-c may begin after the CCA periods of the S′ subframes725-b and 725-c and start with a D subframe, as shown. Because the CCAslot 720-c of the eNB2 is scheduled first in time, the eNB2 has a chanceto reserve the next transmission interval before the eNB1 has a chanceto reserve the next transmission interval. However, because of thepseudo-random CCA slot selection process implemented by each of eNB1 andeNB2, the eNB1 may be provided the first chance to reserve a latertransmission interval (e.g., because its CCA slot may occur at anearlier time than the CCA slot of the eNB2 in a later gating interval).

By way of example, FIG. 10C shows there is WiFi transmission (Tx)activity that coincides with a portion of the aligned CCA periods of theS′ subframes 725-b and 725-c. Because of the timing of the CCA slot720-c selected by the eNB2, the eNB2 may determine as a result ofperforming its CCA that the unlicensed spectrum is unavailable, and maygate OFF a downlink transmission 1005-a in the unlicensed spectrum forthe next transmission interval. A downlink transmission of the eNB2 maytherefore be blocked as a result of the WiFi Tx activity occurringduring performance of the eNB2's CCA.

During the CCA slot 720-b, the eNB1 may perform its CCA. Because of thetiming of the CCA slot 720-b selected by the eNB1, the eNB1 maydetermine as a result of performing its CCA that the unlicensed spectrumis available (e.g., because the WiFi Tx activity does not occur duringthe CCA slot 720-b, and because the eNB2 was not able to reserve thenext transmission interval at an earlier time). The eNB1 may thereforereserve the next transmission interval and gate ON a downlinktransmission 1005 in the unlicensed spectrum for the next transmissioninterval. Methods for reserving the unlicensed spectrum (or a channel ofthe unlicensed spectrum) are described in detail later in thisdescription.

FIGS. 9A, 9B, 10A, 10B, and 10C provide examples of how a CCA slot 720may be selected in the context of a ten millisecond gating interval,such as the gating interval 605-d described with reference to FIG. 7. Incontrast, FIGS. 10D, 10E, 10F, and 10G provide examples of how a CCAslot 720 may be selected in the context of a one or two millisecondgating interval. A gating interval of ten milliseconds may provideadvantages such as a low gating interval overhead in the presence of lowWiFi activity, and an ability to retain the subframe-based PHY channeldesign of existing LTE channels. However, it may have the disadvantageof a long channel idle time (e.g., 0.5+ milliseconds, depending on CCAdelay induced by CCA dithering), which may provide a WiFi node withshort contention window a transmit opportunity (e.g., a transmitopportunity during the guard period 905 described with reference toFIGS. 9A and 9B). It may also have the disadvantage of delaying adownlink transmission at least ten milliseconds when a CCA is notsuccessful. A gating interval of, for example, one or two millisecondsmay lead to a higher gating interval overhead, and may require moreextensive changes to the LTE PHY channel design to supportsub-millisecond transmit durations. However, a gating interval ofperhaps one or two milliseconds may mitigate or eliminate theafore-mentioned disadvantages associated with a ten millisecond gatinginterval.

FIG. 10D provides an example 1000-c of a one millisecond gating interval605-i. A one millisecond gating interval may be used by the basestations 105, 105-a, and 105-b of FIG. 1, FIG. 2A, and FIG. 2B,respectively. The one millisecond gating interval may used in the system100 of FIG. 1 and with portions of the system 200 and/or 200-a shown inFIG. 2A and/or FIG. 2B.

The current LTE specification requires a channel occupancy time (ONtime)≥one millisecond, and a channel idle time five percent of thechannel occupancy time. Thus, the current LTE specification dictates aminimum gating interval duration of 1.05 milliseconds. However, if theLTE specification could be relaxed to require a minimum channeloccupancy time of perhaps 0.95 milliseconds, then a one millisecondgating interval would be possible.

As shown in FIG. 10D, a gating interval 605-i of one millisecond mayinclude 14 OFDM symbols (or symbol positions). When a successful CCA isperformed during a CCA slot 720-d preceding the gating interval 605-i, adownlink transmission may occur during the first 13 OFDM symbols of thegating interval 605-i. Such a downlink transmission may have a duration(or channel occupancy time) of 929 microseconds. In accord with thecurrent LTE standard, a channel occupancy time of 929 microseconds wouldrequire a channel idle time 905-a of 48 microseconds, which is less thanthe 71.4 microsecond duration of one OFDM symbol. As a result, thechannel idle time 905-a of 48 microseconds, as well as one or more CCAslots 720-d, may be provided during the 14^(th) OFDM symbol position. Insome cases, two CCA slots 720-d having a total duration of 20microseconds may be provided during the 14^(th) OFDM symbol position,thereby enabling some amount of CCA randomization (dithering). Of note,each CCA slot 720-d in the example 1000-c has a duration of less thanone OFDM symbol.

Because the CCA slots 720-d are positioned at the end of the onemillisecond gating interval 605-i or subframe shown in FIG. 10D, thegating interval 605-i is common reference signal (CRS) friendly. Anexample 1000-d of a one millisecond gating interval 605-j that isUE-specific reference signal (UERS) friendly is shown in FIG. 10E.Similar to the gating interval 605-i, the gating interval 605-j includes14 OFDM symbols. However, the channel idle time 905-b and CCA slots720-e are provided in the first OFDM symbol position. A successful CCAperformed during a CCA slot 720-e of the current gating interval 605-jthereby enables the unlicensed spectrum to be reserved, and enables adownlink transmission to be made, in the current gating interval. Thenext transmission interval is therefore included within the currentgating interval.

FIG. 10F provides an example 1000-e of a two millisecond gating interval605-k. A two millisecond gating interval may be used by the basestations 105, 105-a, and 105-b of FIG. 1, FIG. 2A, and FIG. 2B,respectively. The two millisecond gating interval may used in the system100 of FIG. 1 and with portions of the system 200 and/or 200-a shown inFIG. 2A and/or FIG. 2B.

In contrast to the one millisecond gating intervals 605-i and 605-j, thetwo millisecond gating interval 605-k complies with the current LTEspecification requirements for maximum channel occupancy time andminimum channel idle time.

As shown, the gating interval 605-k may include a D subframe 710-a andan S′ subframe 725-d. However, the S′ subframe is configured somewhatdifferently than previously described S′ subframes. More particularly,the first 12 OFDM symbol positions of the S′ subframe, as well as the 14OFDM symbol positions of the preceding D subframe, may be used for adownlink transmission upon performing a successful CCA during a CCA slot720-f preceding the gating interval 605-k. The channel occupancy timemay therefore be 1.857 milliseconds, requiring a channel idle time 905-cof 96 microseconds. The channel idle time 905-c may therefore occupy the13^(th) OFDM symbol position of the S′ subframe and part of the 14^(th)OFDM symbol position of the S′ subframe. However, the remaining durationof the 14^(th) OFDM symbol position may be filled, at least in part, bya number of CCA slots 720-f. In some cases, the number of CCA slots720-f may be three CCA slots 720-f, which provides a slightly greateramount of CCA randomization (dithering) than the one millisecond gatingintervals described with reference to FIGS. 10D and 10E.

Because the CCA slots 720-f are positioned at the end of the twomillisecond gating interval 605-k shown in FIG. 10F, the gating interval605-k is CRS friendly. An example 1000-f of a two millisecond gatinginterval 605-1 that is UERS friendly is shown in FIG. 10G. Similar tothe gating interval 605-k, the gating interval 605-1 includes a Dsubframe 725-e and an S′ subframe 710-b. However, the temporal order ofthe subframes is reversed, with the S′ subframe 710-b occurring first intime and the D subframe 725-e occurring later in time. Furthermore, thechannel idle time 905-d and CCA slots 720-g are provided in the firstOFDM symbol position of the S′ subframe 710-b. A successful CCAperformed during a CCA slot 720-g of the current gating interval 605-1thereby enables the unlicensed spectrum to be reserved, and enables adownlink transmission to be made, in the current gating interval. Thenext transmission interval is therefore included within the currentgating interval.

FIG. 11 is a flow chart illustrating an example of a method 1100 forwireless communications. For clarity, the method 1100 is described belowwith reference to one of the eNBs 105 shown in FIGS. 1, 2A, and/or 2B.In one implementation, one of the eNBs 105 may execute one or more setsof codes to control the functional elements of the eNB 105 to performthe functions described below.

At block 1105, a CCA is performed for another unlicensed spectrum in acurrent gating interval to determine whether the unlicensed spectrum isavailable for a downlink transmission in a next transmission interval.Performing the CCA for the unlicensed spectrum may in some cases involveperforming the CCA for one or more channels of the unlicensed spectrum.In some cases, the next transmission interval may be a next gatinginterval. In other cases, the next transmission interval may be includedwithin the current gating interval. In still other cases, such as casesin which an asynchronous LBT-LBE gating interval is used, the nexttransmission interval may follow the current gating interval but not bepart of a next gating interval.

At block 1110, and when a determination is made that the unlicensedspectrum is unavailable, a downlink transmission in the unlicensedspectrum may be gated OFF for the next transmission interval. Otherwise,when a determination is made that the unlicensed spectrum is available,a downlink transmission in the unlicensed spectrum may be gated ON forthe next transmission interval.

In some embodiments of the method 1100, the CCA may be performed duringa first subframe or first or second OFDM symbol position of the currentgating interval. In other embodiments of the method 1100, the CCA may beperformed during a last subframe or last OFDM symbol position of thecurrent gating interval.

In some embodiments of the method 1100, performance of the CCA may besynchronized across multiple eNBs, including multiple eNBs operated by asingle LTE-U operator or by different LTE-U operators.

Thus, the method 1100 may provide for wireless communications. It shouldbe noted that the method 1100 is just one implementation and that theoperations of the method 1100 may be rearranged or otherwise modifiedsuch that other implementations are possible.

FIG. 12A is a flow chart illustrating yet another example of a method1200 for wireless communications. For clarity, the method 1200 isdescribed below with reference to one of the eNBs 105 shown in FIGS. 1,2A, and/or 2B. In one implementation, one of the eNBs 105 may executeone or more sets of codes to control the functional elements of the eNB105 to perform the functions described below.

At block 1205, CCA slots may be synchronized across multiple basestations (e.g., LTE-U eNBs 105) to determine an availability of anunlicensed spectrum (or at least one channel of the unlicensed spectrum)for downlink transmissions in a next transmission interval.

In some embodiments, the CCA slots may be located in a first subframe ora first or second OFDM symbol position of a current gating interval. Inother embodiments, the CCA slots may be located in a last subframe orlast OFDM symbol position of a current gating interval.

In some embodiments, such as embodiments in which a gating interval hasa duration of ten milliseconds, the interval between commencement ofadjacent CCA slots may be approximately the duration of an OFDM symbol.For purposes of this description, “approximately the duration of theOFDM symbol” includes equal to the duration of an OFDM symbol. Anexample in which the interval between commencement of adjacent CCA slotsmay be approximately the duration of an OFDM symbol is shown in FIG. 9B.

Thus, the method 1200 may provide for wireless communications. It shouldbe noted that the method 1200 is just one implementation and that theoperations of the method 1200 may be rearranged or otherwise modifiedsuch that other implementations are possible.

FIG. 12B is a flow chart illustrating another example of a method 1200-afor wireless communications. For clarity, the method 1200-a is describedbelow with reference to one of the eNBs 105 shown in FIGS. 1, 2A, and/or2B. In one implementation, one of the eNBs 105 may execute one or moresets of codes to control the functional elements of the eNB 105 toperform the functions described below.

At block 1215, CCA slots may be synchronized across multiple basestations (e.g., LTE-U eNBs 105) to determine an availability of anunlicensed spectrum (or at least one channel of the unlicensed spectrum)for downlink transmissions in a next transmission interval.

In some embodiments, the CCA slots may be located in a first subframe ora first or second OFDM symbol position of a current gating interval. Inother embodiments, the CCA slots may be located in a last subframe orlast OFDM symbol position of a current gating interval.

In some embodiments, such as embodiments in which a gating interval hasa duration of ten milliseconds, the interval between commencement ofadjacent CCA slots may be approximately the duration of an OFDM symbol.An example in which the interval between commencement of adjacent CCAslots may be approximately a duration of an OFDM symbol is shown in FIG.9B.

At block 1220, one of the CCA slots is identified as a CCA slot in whichto determine the availability of unlicensed spectrum. The one of the CCAslots may be identified based at least in part on a pseudo-randomselection sequence driven by a randomization seed.

In some embodiments, at least a subset of the multiple base stations mayuse the same randomization seed for their pseudo-random sequencegeneration. The subset may be associated with a deployment of basestations by a single operator.

Thus, the method 1200-a may provide for wireless communications. Itshould be noted that the method 1200-a is just one implementation andthat the operations of the method 1200-a may be rearranged or otherwisemodified such that other implementations are possible.

FIG. 13A is a flow chart illustrating another example of a method 1300for wireless communications. For clarity, the method 1300 is describedbelow with reference to one of the eNBs 105 shown in FIGS. 1, 2A, and/or2B. In one implementation, one of the eNBs 105 may execute one or moresets of codes to control the functional elements of the eNB 105 toperform the functions described below.

At block 1305, a CCA may be performed during one of multiple CCA slotssynchronized across multiple eNBs 105 (e.g., LTE-U eNBs) to determine anavailability of an unlicensed spectrum (or at least one channel of theunlicensed spectrum) for downlink transmissions in a next transmissioninterval.

In some embodiments, different eNBs may use different ones of themultiple CCA slots to perform CCA during a gating interval. In otherembodiments, two or more eNBs may use the same CCA slot to perform CCAduring a gating interval (e.g., when there exists coordination between asubset of eNBs, such as coordination between the eNBs deployed by asingle operator).

Thus, the method 1300 may provide for wireless communications. It shouldbe noted that the method 1300 is just one implementation and that theoperations of the method 1300 may be rearranged or otherwise modifiedsuch that other implementations are possible.

FIG. 13B is a flow chart illustrating yet another example of a method1300-a for wireless communications. For clarity, the method 1300-a isdescribed below with reference to one of the eNBs 105 shown in FIGS. 1,2A, and/or 2B. In one implementation, one of the eNBs 105 may executeone or more sets of codes to control the functional elements of the eNB105 to perform the functions described below.

At block 1315, a CCA slot may be identified (e.g., by an eNB) from amongmultiple CCA slots synchronized across multiple eNBs 105 (e.g., LTE-UeNBs). The slot may be identified based at least in part on apseudo-random selection sequence generated from a randomization seed. Inalternate embodiment, the slot may be identified based at least in parton coordination information exchanged between at least a subset of theeNBs over a backhaul, such as the backhaul 132 or 134 described withreference to FIG. 1.

At block 1320, a CCA may be performed during the identified CCA slot todetermine an availability of an unlicensed spectrum (or at least onechannel of the unlicensed spectrum) for downlink transmissions in a nexttransmission interval.

In some embodiments, different eNBs may identify different ones ofmultiple CCA slots to perform CCA during a gating interval. In otherembodiments, two or more eNBs may identify the same CCA slot to performCCA during a gating interval.

Thus, the method 1300-a may provide for wireless communications. Itshould be noted that the method 1300-a is just one implementation andthat the operations of the method 1300-a may be rearranged or otherwisemodified such that other implementations are possible.

FIG. 14A provides another example 1400 of how the performance of CCAsfor an unlicensed spectrum (or a channel of the unlicensed spectrum) maybe synchronized across multiple eNBs 105. Examples of the eNBs 105 maybe the base stations 105, 105-a, and 105-b of FIG. 1, FIG. 2A, and FIG.2B, respectively. The performance of CCAs may in some examples besynchronized across the eNBs 105 used in the system 100 of FIG. 1, orwith portions of the system 100 shown in FIG. 2A and FIG. 2B.

FIG. 14A also shows how the unlicensed spectrum may be reserved by oneor more of the eNBs 105 following a successful CCA. By way of example,the multiple eNBs 105 may include an LTE-U eNB1, an LTE-U eNB2, and anLTE-U eNB3.

As shown, the boundaries of the current gating intervals of each eNB(e.g., eNB1, eNB2, and eNB3) may be synchronized, thereby providingsynchronization of the S′ subframes 725-f, 725-g, 725-h of the eNBs. ACCA period of each S′ subframe may include multiple CCA slots 720.Because of a synchronized pseudo-random CCA slot selection processesimplemented by each eNB, the eNB2 may select a CCA slot 720-i thatoccurs at a different time (e.g., different OFDM symbol position) thanthe CCA slot 720-h selected by eNB1. For example, the eNB1 may select aCCA slot 720-h aligned with the fifth OFDM symbol position of thealigned CCA periods of the S′ subframes 725-f and 725-g, and the eNB2may select a CCA slot 720-i aligned with the third OFDM symbol positionof the aligned CCA periods. However, when the eNB3 is deployed by thesame operator as the eNB1, the eNB3 may synchronize the timing of itsCCA slot 720-j with the timing of the CCA slot 720-h selected for eNB1.The operator deploying both eNB1 and eNB3 may then determine which eNBis allowed access to the unlicensed spectrum or coordinate simultaneousaccess to the unlicensed spectrum by virtue of orthogonal transmissionsand/or other transmission mechanisms.

A next transmission interval following the synchronized S′ subframes725-f, 725-g, 725-h may begin after the CCA periods of the S′ subframes725-f, 725-g, 725-h and start with a D subframe, as shown. Because theCCA slot 720-i of the eNB2 is scheduled first in time, the eNB2 has achance to reserve the next transmission interval before the eNB1 andeNB3 have a chance to reserve the next transmission interval. However,because of the pseudo-random CCA slot selection process implemented byeach of eNB1, eNB1, and eNB3, the eNB1 or eNB3 may be provided the firstchance to reserve a later transmission interval.

By way of example, FIG. 14A shows there is WiFi transmission (Tx)activity that coincides with a portion of the aligned CCA periods of theS′ subframes 725-f, 725-g, 725-h. Because of the timing of the CCA slot720-i selected by the eNB2, the eNB2 may determine as a result ofperforming its CCA that the unlicensed spectrum is unavailable, and maygate OFF a downlink transmission 1005-c in the unlicensed spectrum forthe next transmission interval. A downlink transmission of the eNB2 maytherefore be blocked as a result of the WiFi Tx activity occurringduring performance of the eNB2's CCA.

During the CCA slots 720-h and 720-j, the eNB1 and the eNB3 may eachperform their respective CCA. Because of the timing of the CCA slots720-h, 720-j selected by the eNB1 and the eNB3, each of the eNB1 and theeNB3 may determine as a result of performing their CCA that theunlicensed spectrum is available (e.g., because the WiFi Tx activitydoes not occur during the CCA slots 720-h, 720-i, and because the eNB2was not able to reserve the next transmission interval at an earliertime). The eNB1 and the eNB3 may therefore each reserve the nexttransmission interval and gate ON a downlink transmission 1005-b, 1005-din the unlicensed spectrum for the next transmission interval.

An eNB may reserve the next transmission interval by transmitting one ormore signals before the next transmission interval to reserve theunlicensed spectrum during the next transmission interval. For example,after determining that the unlicensed spectrum is available (e.g., byperforming a successful CCA), the eNB1 may fill each of the CCA slotsfollowing its performance of a successful CCA with CUBS 1010-a. The CUBS1010-a may include one or more signals that are detectable by otherdevices to let the other devices know the unlicensed spectrum (or atleast a channel thereof) has been reserved for use by another device(e.g., by the eNB1). The CUBS 1010-a may be detected by both LTE andWiFi devices. Unlike most LTE signals, which begin at a subframeboundary, the CUBS 1010-a may begin at an OFDM symbol boundary.

In some cases, the CUBS 1010-a may include a placeholder signaltransmitted for the purpose of reserving the unlicensed spectrum. Inother cases, the CUBS 1010-a may include, for example, at least onepilot signal for one or both of time-frequency synchronization andchannel quality estimation over the unlicensed spectrum. The pilotsignal(s) may be used by one or more UEs 115 to make channel qualitymeasurements on different resource elements, so that a channel qualitymay be reported to the eNB1. The eNB1 may then receive the report ofchannel quality from the UE 115 in response to the CUBS 1010-a, andallocate resource elements for transmissions from the eNB1 to the UE 115to provide fractional resource reuse among multiple UEs 115, to avoidinterference among the multiple UEs 115.

In some embodiments, the CUBS 1010-a may be transmitted repetitively,with the transmission of each signal starting at a boundary of one ofthe multiple CCA slots.

In some embodiments, it may be ensured that at least one OFDM symbolposition worth of CUBS is transmitted following a successful CCA, toassist in time/frequency synchronization between a transmitting LTE-UeNB and a receiving UE.

In some embodiments, and when there is a duration of more than two OFDMsymbols between a successful CCA and the start of a next transmissioninterval, the third and subsequent CUBS transmissions may be modified tocarry downlink data and control information from the transmitting LTE-UeNB to a receiving UE.

In some embodiments, the CUBS 1010-a may be modeled after the downlinkpilot time slot (DwPTS) structure defined in the current LTEspecification.

In some embodiments, the CUBS 1010-a may include a wideband waveformthat carries a signature sequence determined by the DeploymentID of thetransmitting LTE-U eNB. The signature sequence may be a known sequencehaving low information content, and hence be IC-friendly for LTE-Ureceiver nodes. The wideband waveform may in some cases be transmittedat full transmit power, to overcome the transmit power spectral density(Tx-PSD) and minimum bandwidth (min-BW) constraints, as well as silenceother nodes (e.g., WiFi nodes).

The eNB3 may likewise fill each of the CCA slots following itsperformance of a successful CCA with CUBS 1010-b, and may receive areport of channel quality from a different one of the UEs 115.

FIG. 14B provides yet another example 1400-a of how the performance ofCCAs for an unlicensed spectrum (or a channel of the unlicensedspectrum) may be synchronized across multiple eNBs 105. Examples of theeNBs 105 may be the base stations 105, 105-a, and 105-b of FIG. 1, FIG.2A, and FIG. 2B, respectively. The performance of CCAs may in someexamples be synchronized across the eNBs 105 used in the system 100 ofFIG. 1, or with portions of the system 100 shown in FIG. 2A and FIG. 2B.

FIG. 14B also shows how the unlicensed spectrum may be reserved by oneof the eNBs 105 following a successful CCA. By way of example, themultiple eNBs 105 may include an LTE-U eNB1, an LTE-U eNB2, and an LTE-UeNB4.

As shown, the boundaries of the current gating intervals of each eNB(e.g., eNB1, eNB2, and eNB4) may be synchronized, thereby providingsynchronization of the S′ subframes 725-f, 725-g, 725-i of the eNBs. ACCA period of each S′ subframe may include multiple CCA slots 720.Because of a synchronized pseudo-random CCA slot selection processesimplemented by each eNB, the eNB2 may select a CCA slot 720-i thatoccurs at a different time (e.g., different OFDM symbol position) thanthe CCA slot 720-h selected by eNB1. For example, the eNB1 may select aCCA slot 720-h aligned with the fifth OFDM symbol position of thealigned CCA periods of the S′ subframes 725-f and 725-g, and the eNB2may select a CCA slot 720-i aligned with the third OFDM symbol positionof the aligned CCA periods. Likewise, the eNB4 may select a CCA slot720-k that occurs at a different time than the CCA slots 720-h, 720-iselected by each of the eNB1 and the eNB2 (e.g., because the eNB4 maynot be deployed by the same operator as the eNB1, as was the case withthe eNB3 described with reference to FIG. 14A). For example, the eNB4may select a CCA slot 720-k aligned with the sixth OFDM symbol positionof the aligned CCA periods.

A next transmission interval following the synchronized S′ subframes725-f, 725-g, 725-i may begin after the CCA periods of the S′ subframes725-f, 725-g, 725-i and start with a D subframe, as shown. Because theCCA slot 720-i of the eNB2 is scheduled first in time, the eNB2 has achance to reserve the next transmission interval before the eNB1 andeNB4 have a chance to reserve the next transmission interval. However,because of the pseudo-random CCA slot selection process implemented byeach of the eNB1, the eNB2, and the eNB4, the eNB1 or the eNB4 may beprovided the first chance to reserve a later transmission interval.

By way of example, FIG. 14B shows there is WiFi transmission (Tx)activity that coincides with a portion of the aligned CCA periods of theS′ subframes 725-f, 725-g, 725-i. However, because the WiFi Tx activitydoes not coincide with the timing of the CCA slot 720-i selected by theeNB2, the eNB2 may determine as a result of performing its CCA that theunlicensed spectrum is available, and may gate ON a downlinktransmission 1005-c in the unlicensed spectrum for the next transmissioninterval. Also, and following its successful CCA, the eNB2 may fill thesubsequent CCA slots with CUBS 1010-c, thereby reserving the nexttransmission interval for its own use.

During the CCA slots 720-h and 720-k, the eNB1 and the eNB4 may eachperform their respective CCA. However, because the eNB2 has alreadybegun to transmit CUBS 1010-c, the eNB1 and the eNB4 determine that theunlicensed spectrum is unavailable. Stated another way, the eNB1 and theeNB4 are blocked from the unlicensed spectrum by virtue of the eNB2already having reserved the unlicensed spectrum.

FIG. 14C provides yet another example 1400-b of how the performance ofCCAs for an unlicensed spectrum (or a channel of the unlicensedspectrum) may be synchronized across multiple eNBs 105. Examples of theeNBs 105 may be the base stations 105, 105-a, and 105-b of FIG. 1, FIG.2A, and FIG. 2B, respectively. The performance of CCAs may in someexamples be synchronized across the eNBs 506 used in the system 100 ofFIG. 1, or with portions of the system 100 shown in FIG. 2A and FIG. 2B.

FIG. 14C also shows how the unlicensed spectrum may be reserved by oneof the eNBs 105 following a successful CCA. By way of example, themultiple eNBs 105 may include an LTE-U eNB1, an LTE-U eNB2, and an LTE-UeNB4.

As shown, the boundaries of the current gating intervals of each eNB(e.g., eNB1, eNB2, and eNB4) may be synchronized, thereby providingsynchronization of the S′ subframes 725-f, 725-g, 725-i of the eNBs. ACCA period of each S′ subframe may include multiple CCA slots 720.Because of a synchronized pseudo-random CCA slot selection processesimplemented by each eNB, the eNB2 may select a CCA slot 720-i thatoccurs at a different time (e.g., different OFDM symbol position) thanthe CCA slot 720-h selected by eNB1. For example, the eNB1 may select aCCA slot 720-h aligned with the fifth OFDM symbol position of thealigned CCA periods of the S′ subframes 725-f and 725-g, and the eNB2may select a CCA slot 720-i aligned with the third OFDM symbol positionof the aligned CCA periods. Likewise, the eNB4 may select a CCA slot720-k that occurs at a different time than the CCA slots 720-h, 720-iselected by each of the eNB1 and the eNB2 (e.g., because the eNB3 maynot be deployed by the same operator as the eNB1, as was the case in theexample described with reference to FIG. 14A). For example, the eNB4 mayselect a CCA slot 720-k aligned with the sixth OFDM symbol position ofthe aligned CCA periods.

A next transmission interval following the synchronized S′ subframes725-f, 725-g, 725-i may begin after the CCA periods of the S′ subframes725-f, 725-g, 725-i and start with a D subframe, as shown. Because theCCA slot 720-i of the eNB2 is scheduled first in time, the eNB2 has achance to reserve the next transmission interval before the eNB1 andeNB4 have a chance to reserve the next transmission interval. However,because of the pseudo-random CCA slot selection process implemented byeach of the eNB1, the eNB2, and the eNB4, the eNB1 or the eNB4 may beprovided the first chance to reserve a later transmission interval.

By way of example, FIG. 14C shows there is WiFi transmission (Tx)activity that coincides with a portion of the aligned CCA periods of theS′ subframes 725-f, 725-g, 725-i. Because of the timing of the CCA slot720-i selected by the eNB2, the eNB2 may determine as a result ofperforming its CCA that the unlicensed spectrum is unavailable, and maygate OFF a downlink transmission 1005-c in the unlicensed spectrum forthe next transmission interval. A downlink transmission of the eNB2 maytherefore be blocked as a result of the WiFi Tx activity occurringduring performance of the eNB2's CCA.

During the CCA slot 720-h, the eNB1 may perform its CCA and determinethat the unlicensed spectrum is available (e.g., because the WiFi Txactivity does not occur during the CCA slot 720-h, and because the eNB2was not able to reserve the next transmission interval at an earliertime). The eNB1 may therefore reserve the next transmission interval andgate ON a downlink transmission 1005-b in the unlicensed spectrum forthe next transmission interval. Also, and following its successful CCA,the eNB1 may fill the subsequent CCA slots with CUBS 1010-d, therebyreserving the next transmission interval for its own use.

During the CCA slot 720-k, the eNB4 may perform its CCA and detect theCUBS 1010-d. As a result, the eNB4 may determine that the unlicensedspectrum is unavailable and gate OFF a downlink transmission 1005-d inthe unlicensed spectrum. Stated another way, the eNB4 is blocked fromthe unlicensed spectrum by virtue of the eNB1 already having reservedthe unlicensed spectrum.

In FIGS. 14A, 14B, and 14C, CUBS 1010 are transmitted prior to a nexttransmission interval, to reserve unlicensed spectrum for an LTE-U eNB'suse during the next transmission interval. However, in some embodiments,CUBS 1010 may be transmitted at the beginning of an active transmissioninterval to provide, for example, time/frequency synchronization for anLTE-U eNB and UE that are in communication during the activetransmission interval.

In some embodiments, CUBS may be transmitted for less than the durationan OFDM symbol. Transmissions of CUBS for less than an OFDM symbol maybe referred to as partial CUBS (PCUBS). By way of example, and in thecontext of the one or two millisecond gating intervals described withreference to FIGS. 10D, 10E, 10F, and 10G, PCUBS may be transmittedbetween the performance of a successful CCA and the start of a next OFDMsymbol boundary. In some embodiments, PCUBS may be obtained from a fullsymbol CUBS by puncturing three out of every four tones and truncatingthe CUBS to a desired duration. Alternately, PCUBS may be formed by aphysical layer convergence procedure (PLCP) preamble and header based onthe IEEE 802.11g/n standard (which can silence at least standardcompliant WiFi nodes).

FIG. 15 is a flow chart illustrating an example of a method 1500 forwireless communications. For clarity, the method 1500 is described belowwith reference to one of the eNBs 105 shown in FIGS. 1, 2A, and/or 2B.In one implementation, one of the eNBs 105 may execute one or more setsof codes to control the functional elements of the eNB 105 to performthe functions described below.

At block 1505, a CCA may be performed during one of multiple CCA slotssynchronized across multiple eNBs 105 (e.g., LTE-U eNBs) to determine anavailability of an unlicensed spectrum (or at least one channel of theunlicensed spectrum) for downlink transmissions in a next transmissioninterval.

In some embodiments, different eNBs may use different ones of themultiple CCA slots to perform CCA during a gating interval. In otherembodiments, two or more eNBs may use the same CCA slot to perform CCAduring a gating interval (e.g., when there exists coordination between asubset of eNBs, such as coordination between the eNBs deployed by asingle operator).

At block 1510, and when the unlicensed spectrum is available (e.g., whenit is determined by performing a successful CCA that the unlicensedspectrum is available), one or more signals may be transmitted beforethe next transmission interval to reserve the unlicensed spectrum duringthe next transmission level. In some cases, the one or more signals mayinclude CUBS 1010, as described with reference to FIGS. 14A, 14B, and/or14C.

In some embodiments, the one or more signals transmitted before the nexttransmission interval may include at least one pilot signal for one orboth of time-frequency synchronization and channel quality estimationover the unlicensed spectrum. The pilot signal(s) may be used by one ormore UEs 115 to make channel quality measurements on different resourceelements, so that a channel quality may be reported to the eNB 105 thattransmitted the one or more signals. The eNB 105 may then receive thereport of channel quality from the UE 115 in response to the pilotsignal(s) and allocate resource elements for transmissions from the eNB105 to the UE 115 to provide fractional resource reuse among multipleUEs 115, to avoid interference among the multiple UEs 115.

Thus, the method 1500 may provide for wireless communications. It shouldbe noted that the method 1500 is just one implementation and that theoperations of the method 1500 may be rearranged or otherwise modifiedsuch that other implementations are possible.

When gating access to an unlicensed spectrum, gating intervals may forcean LTE-U eNB to be silent for several LTE radio frames. Because of this,an LTE-U eNB that relies on conventional LTE reporting of feedbackinformation (e.g., channel state information (CSI)) may not haveup-to-date channel quality indicator (CQI) information before schedulinga downlink transmission. An LTE-U eNB that relies on conventional LTEreporting of feedback information may also fail to receive hybridautomatic repeat requests (HARQ) in a timely fashion. Mechanisms thattake gating intervals of an unlicensed spectrum into account, and reportCSI and HARQ over gated OFF transmission intervals of a downlink in theunlicensed spectrum, may therefore be used to improve the LTE-U eNB'sCQI and HARQ processing. Examples of such mechanisms are described withreference to FIGS. 16, 17A, and 17B.

FIG. 16 is a diagram 1600 illustrating communications between an eNB105-c and a UE 115-c. The eNB 105-c may be an example of the basestations 105, 105-a, and 105-b of FIG. 1, FIG. 2A, and FIG. 2B,respectively. The UE 115-c may be an example of the UEs 115, 115-a, and115-b of FIG. 1, FIG. 2A, and FIG. 2B, respectively. The eNB 105-c andthe UE 115-c may used in the system 100 of FIG. 1 and with portions ofthe system 100 shown in FIG. 2A and FIG. 2B.

The eNB 105-c may communicate with the UE 115-c via a downlink 1610 inan unlicensed spectrum, and the UE 115-c may communicate with the eNB105-c via a primary component carrier (PCC) uplink 1605 in a licensedspectrum. The UE 115-c may transmit feedback information to the eNB105-c via the PCC uplink 1605, and the eNB 105-c may receive thefeedback information from the UE 115-c via the PCC uplink 1605. In somecases, the feedback information may address (or pertain to) signalstransmitted from the eNB 105-c to the UE 115-c via the downlink 1610.Transmitting feedback information for the unlicensed spectrum via thelicensed spectrum may improve the reliability of feedback informationfor the unlicensed spectrum.

The feedback information may in some cases include feedback informationfor at least one transmission interval gated from the downlink 1610.

In some embodiments, the feedback information may include channel stateinformation (CSI), such as CSI for the downlink 1610. For at least onetransmission interval during which the eNB 105-c gated OFF transmissionsfor the downlink 1610, the CSI may include long-term CSI. However, forat least one transmission interval during which the eNB 105-c gated ONtransmissions for the downlink, the CSI may include short-term CSI. Thelong-term CSI may include, for example, radio resource management (RRM)information that captures the details of the channel interferenceenvironment (e.g., information identifying each source of dominantinterference, whether it be a WiFi, station (STA), and/or LTE-U eNB, forexample; information identifying the average strength and/or spatialcharacteristics of each interfering signal; etc.). The short-term CSImay include, for example, a CQI, a rank indicator (RI), and/or apre-coding matrix indicator. In some cases, the CSI may be sent from aUE 115 to an eNB 115, via the PCC uplink 1605, in a second subframefollowing the start of downlink transmissions in a current transmissioninterval in the unlicensed spectrum.

In some embodiments, the feedback information may include HARQ feedbackinformation, such as HARQ feedback information for the downlink 1610. Inone example of HARQ transmission, HARQ may ignore transmission intervalswhere downlink transmissions were gated OFF. In another example of HARQtransmission, HARQ may be used for transmission intervals where downlinktransmissions are gated ON, and a simple automated repeat request (ARQ)may be used for transmission intervals where downlink transmissions aregated OFF. Both examples may retain almost full HARQ functionality inthe context of a single LTE-U deployment with no WiFi interference.However, in the presence of WiFi interference or multiple LTE-Udeployments (e.g., deployments by different operators), the secondexample may be forced to predominantly use ARQ, in which case CSI maybecome the main tool for link adaptation. Asynchronous HARQ may betransmitted in a manner that is unaffected by gating of the unlicensedspectrum.

When a downlink transmission is not acknowledged (NAK'd), a best effortHARQ retransmission may be made via the downlink 1610. However, after atimeout period, the NAK'd packet may be recovered through radio linkcontrol (RLC) retransmissions via the downlink 1610 or a PCC downlink.

The eNB 105-c may in some cases use both the long-term CSI and theshort-term CSI to select a modulation and coding scheme (MCS) for thedownlink 1610 in the unlicensed spectrum. The HARQ may then be used tofine-tune the served spectral efficient of the downlink 1610 inreal-time.

FIG. 17A is a flow chart illustrating an example of another method 1700for wireless communications. For clarity, the method 1700 is describedbelow with reference to one of the eNBs 105 shown in FIGS. 1, 2A, and/or2B. In one implementation, one of the eNBs 105 may execute one or moresets of codes to control the functional elements of the eNB 105 toperform the functions described below.

At block 1705, feedback information is received (e.g., by an eNB 105)from a UE 115 via a PCC uplink in a licensed spectrum. The feedbackinformation may include information that addresses (or pertains to)signals transmitted to the UE 115 via a downlink in an unlicensedspectrum.

The feedback information may in some cases include feedback informationfor at least one transmission interval gated from the downlink 1610.

In some embodiments, the feedback information may include channel stateinformation (CSI), such as CSI for the downlink 1610. For at least onetransmission interval during which the eNB 105-c gated OFF transmissionsfor the downlink 1610, the CSI may include long-term CSI. However, forat least one transmission interval during which the eNB 105-c gated ONtransmissions for the downlink, the CSI may include short-term CSI. Thelong-term CSI may include, for example, radio resource management (RRM)information that captures the details of the channel interferenceenvironment (e.g., information identifying each source of dominantinterference, whether it be a WiFi, station (STA), and/or LTE-U eNB, forexample; information identifying the average strength and/or spatialcharacteristics of each interfering signal; etc.). The short-term CSImay include, for example, a CQI, a rank indicator (RI), and/or apre-coding matrix indicator. In some cases, the CSI may be sent from aUE 115 to an eNB 115, via the PCC uplink 1605, in a second subframefollowing the start of downlink transmissions in a current transmissioninterval in the unlicensed spectrum.

In some embodiments, the feedback information may include HARQ feedbackinformation, such as HARQ feedback information for the downlink 1610. Inone example of HARQ transmission, HARQ may ignore transmission intervalswhere downlink transmissions were gated OFF. In another example of HARQtransmission, HARQ may be used for transmission intervals where downlinktransmissions are gated ON, and a simple automated repeat request (ARQ)may be used for transmission intervals where downlink transmissions aregated OFF. Both examples may retain almost full HARQ functionality inthe context of a single LTE-U deployment with no WiFi interference.However, in the presence of WiFi interference or multiple LTE-Udeployments (e.g., deployments by different operators), the secondexample may be forced to predominantly use ARQ, in which case CSI maybecome the main tool for link adaptation. Asynchronous HARQ may betransmitted in a manner that is unaffected by gating of the unlicensedspectrum.

When a downlink transmission is not acknowledged (NAK'd), a best effortHARQ retransmission may be made via the downlink 1610. However, after atimeout period, the NAK'd packet may be recovered through radio linkcontrol (RLC) retransmissions via the downlink 1610 or a PCC downlink.

The eNB 105-c may in some cases use both the long-term CSI and theshort-term CSI to select a modulation and coding scheme (MCS) for thedownlink 1610 in the unlicensed spectrum. The HARQ may then be used tofine-tune the served spectral efficient of the downlink 1610 inreal-time.

Thus, the method 1700 may provide for wireless communications. It shouldbe noted that the method 1700 is just one implementation and that theoperations of the method 1700 may be rearranged or otherwise modifiedsuch that other implementations are possible.

FIG. 17B is a flow chart illustrating an example of a method 1700-a forwireless communications. For clarity, the method 1700-a is describedbelow with reference to one of the UEs 115 shown in FIGS. 1, 2A, and/or2B. In one implementation, one of the UEs 115 may execute one or moresets of codes to control the functional elements of the UE 115 toperform the functions described below.

At block 1715, feedback information may be transmitted (e.g., from a UE115) to an eNB 105 via a PCC uplink in a licensed spectrum. The feedbackinformation may include information that addresses (or pertains to)signals transmitted to the UE 115 via a downlink in an unlicensedspectrum.

The feedback information may in some cases include feedback informationfor at least one transmission interval gated from the downlink 1610.

In some embodiments, the feedback information may include channel stateinformation (CSI), such as CSI for the downlink 1610. For at least onetransmission interval during which the eNB 105-c gated OFF transmissionsfor the downlink 1610, the CSI may include long-term CSI. However, forat least one transmission interval during which the eNB 105-c gated ONtransmissions for the downlink, the CSI may include short-term CSI. Thelong-term CSI may include, for example, radio resource management (RRM)information that captures the details of the channel interferenceenvironment (e.g., information identifying each source of dominantinterference, whether it be a WiFi, station (STA), and/or LTE-U eNB, forexample; information identifying the average strength and/or spatialcharacteristics of each interfering signal; etc.). The short-term CSImay include, for example, a CQI, a rank indicator (RI), and/or apre-coding matrix indicator. In some cases, the CSI may be sent from aUE 115 to an eNB 115, via the PCC uplink 1605, in a second subframefollowing the start of downlink transmissions in a current transmissioninterval in the unlicensed spectrum.

In some embodiments, the feedback information may include HARQ feedbackinformation, such as HARQ feedback information for the downlink 1610. Inone example of HARQ transmission, HARQ may ignore transmission intervalswhere downlink transmissions were gated OFF. In another example of HARQtransmission, HARQ may be used for transmission intervals where downlinktransmissions are gated ON, and a simple automated repeat request (ARQ)may be used for transmission intervals where downlink transmissions aregated OFF. Both examples may retain almost full HARQ functionality inthe context of a single LTE-U deployment with no WiFi interference.However, in the presence of WiFi interference or multiple LTE-Udeployments (e.g., deployments by different operators), the secondexample may be forced to predominantly use ARQ, in which case CSI maybecome the main tool for link adaptation. Asynchronous HARQ may betransmitted in a manner that is unaffected by gating of the unlicensedspectrum.

When a downlink transmission is not acknowledged (NAK'd), a best effortHARQ retransmission may be made via the downlink 1610. However, after atimeout period, the NAK'd packet may be recovered through radio linkcontrol (RLC) retransmissions via the downlink 1610 or a PCC downlink.

The eNB 105-c may in some cases use both the long-term CSI and theshort-term CSI to select a modulation and coding scheme (MCS) for thedownlink 1610 in the unlicensed spectrum. The HARQ may then be used tofine-tune the served spectral efficient of the downlink 1610 inreal-time.

Thus, the method 1700-a may provide for wireless communications. Itshould be noted that the method 1700-a is just one implementation andthat the operations of the method 1700-a may be rearranged or otherwisemodified such that other implementations are possible.

Turning next to FIG. 18A, a diagram 1800 illustrates an example of LTE-Ubeacon signal broadcasting in an unlicensed spectrum according tovarious embodiments. The LTE-U beacon signal (or discovery beacons) 1805may be transmitted or broadcast by an eNB that supports LTE-U. Examplesof such an eNB may be the base stations 105, 105-a, and 105-b of FIG. 1,FIG. 2A, and FIG. 2B, respectively. The broadcasting may be performed inconnection with a system or network like the system 100 of FIG. 1 andthe portions of the system 100 of FIG. 2A and FIG. 2B.

The transmissions may occur when the eNB is in an active state or whenthe eNB is in a dormant or inactive state. The beacon signals 1805 maybe transmitted at a low duty cycle (e.g., 1 or 2 subframes every 100milliseconds) and may span up to about 5 Megahertz (MHz) in bandwidth.Because of their low duty cycle, the beacon signals 1805 may betransmitted without the need for a listen-before-talk (LBT) scheme.Accordingly, the beacon signals 1805 may be transmitted (e.g.,broadcast) at predetermined times. In the example shown in FIG. 18A,beacon signals 1805 may be transmitted at least at times t₀, t₁, t₂, andt₃. The timing of these transmissions may be periodic. In some cases thetransmissions may not need to be periodic as long as the times arescheduled (e.g., predetermined) and the schedule may be known to thedevices or entities listening for the beacon signals 1805. The beaconsignals 1805 may be used by other eNBs and/or by UEs (e.g., UEs 115) fordormant/active eNB discovery and for coarse time-frequency tracking.

FIG. 18B shows a diagram 1800-a that illustrates an example of a payloadin an LTE beacon signal according to various embodiments. The beaconsignal 1805-a shown in FIG. 18B may be an example of the beacon signals1805 of FIG. 18A. Accordingly, the beacon signal 1805-a may betransmitted or broadcast by an eNB that supports LTE-U (LTE-U eNB).Examples of such an eNB may be the base stations 105, 105-a, and 105-bof FIG. 1, FIG. 2A, and FIG. 2B, respectively.

A payload of the beacon signal 1805-a may include multiple fields ofinformation or attributes associated with an eNB. For example, thebeacon signal 1805-a may include one or more of a primarysynchronization signal (PSS) field 1810, a secondary synchronizationsignal (SSS) field 1815, a cell-specific reference signal (CRS) field1820, a physical broadcast channel (PBCH) field 1825, a systeminformation block (SIB) field 1830, a closed subscriber group identity(CSG-ID) field 1835, a public land mobile network identifier (PLMN ID)field 1840, a global cell ID (GCI) field 1845, a clear channelassessment randomization seed (CCA-RS) field 1850, a random accesschannel (RACH) configuration field 1855, a light- or lite-version of anSIB (SIB-lite) field 1860, and a deployment ID field 1865. In someembodiments, the SIB-lite field 1860 may include the GCI field 1845 andthe CSG-ID field 1835. The GCI field 1845 may include the PLMN ID field1840. The payload contents shown in FIG. 18B need not be exhaustive.Other information or attributes associated with an eNB may be includedto enable the use of LTE-based communications in an unlicensed spectrum.For example, the payload of the beacon signal 1805-a may include aperiodic gating structure configuration for use in gating ON/OFF a nextgating or transmission interval. Moreover, some of the fields shown neednot be transmitted in some cases and some of the fields may be combined.

The combination of information on the PLMN ID field 1840 and in theCSG-ID field 1835 may be used to identify an LTE-U deploymentconfiguration (e.g., an eNB deployment configuration) for the LTE-Udeployment (e.g., an eNB deployment) associated with a given eNB. Forexample, LTE-U eNBs deployed by different cellular operators may havedifferent PLMN IDs. Some PLMN IDs may be reserved for non-operatordeployment of LTE-U. For example, an LTE-U eNB deployed by anon-operator/enterprise may use a reserved PLMN ID together with aunique CSG-ID.

FIG. 19A shows a flowchart of a method 1900 for broadcasting LTE beaconsignals in an unlicensed spectrum according to various embodiments. Themethod 1900 may be implemented using, for example, the base stations oreNBs 105, 105-a, and 105-b of FIG. 1, FIG. 2A, and FIG. 2B,respectively; and/or the system 100 of FIG. 1 and the portions of thesystem 100 of FIG. 2A and FIG. 2B. In one implementation, one of theeNBs 105 may execute one or more sets of codes to control the functionalelements of the eNB 105 to perform the functions described below.

At block 1905, beacon signals (e.g., beacon signals 1805) may bebroadcast in an unlicensed spectrum at predetermined times from an eNB,where the beacon signals include downlink signals that identify the eNBand at least one associated attribute of the eNB. The beacon signals mayin some cases be received at a UE (or at a plurality of UEs). In someembodiments, a UE may use the beacon signals to make a coarse timingadjustment to communicate in the unlicensed spectrum at the UE.

In some embodiments of the method 1900, the at least one associatedattribute of the eNB may include at least attribute of the eNB. In someembodiments, the at least one associated attribute of the eNB mayinclude an eNB deployment configuration for an eNB deployment with whichthe eNB is associated. In some embodiments, the at least one associatedattribute of the eNB may include an eNB deployment configuration for aneNB deployment with which the eNB is associated, wherein downlinksignals from eNBs in the eNB deployment are synchronized andconcurrently transmitted by the eNBs of the eNB deployment in theunlicensed spectrum and in a licensed spectrum. In some embodiments, theeNBs in the eNB deployment are each deployed by a same operator.

In some embodiments of the method 1900, the at least one associatedattribute of the eNB may include a RACH configuration associated withthe eNB. In these embodiments, the beacon signals may also include apaging message for at least one UE. Upon receiving a beacon signalbroadcast in the unlicensed spectrum, a UE may respond to the pagingmessage using the RACH configuration.

In some embodiments of the method 1900, broadcasting the beacon signalsincludes broadcasting the beacon signals at a duty cycle below 5% (e.g.,1-2%), with a maximum broadcasting interval of approximately once every50 milliseconds. In some embodiments, the beacon signals include one ormore of a PSS, an SSS, a CRS, a PBCH, a CGI, a CSG-ID, a PLMN ID, adeployment ID, a periodic gating structure configuration, a CCA-RS, aRACH configuration, an SIB, and an SIB-lite. The beacon signals mayinclude information that identifies the eNB as being active or dormant.

FIG. 19B shows a flowchart of a method 1900-a for broadcasting LTEbeacon signals in an unlicensed spectrum according to variousembodiments. The method 1900-a, like the method 1900 above, may beimplemented using, for example, the base stations or eNBs 105, 105-a,and 105-b of FIG. 1, FIG. 2A, and FIG. 2B, respectively; and/or thesystem 100 of FIG. 1 and the portions of the system 100 of FIG. 2A andFIG. 2B. In one implementation, one of the eNBs 105 may execute one ormore sets of codes to control the functional elements of the eNB 105 toperform the functions described below.

At block 1915, an eNB deployment is identified in which downlink signalsfrom the deployed eNBs are synchronized and concurrently transmitted bythe deployed eNBs in an unlicensed spectrum and in a licensed spectrum.

At block 1920, beacons signals (e.g., beacon signals 1805) may bebroadcast in an unlicensed spectrum at predetermined times from one ormore of the deployed eNBs, where the beacon signals include theidentified eNB deployment.

Turning next to FIG. 20, a diagram 2000 is shown that illustrates anexample of request-to-send (RTS) and clear-to-send (CTS) signals in anunlicensed spectrum according to various embodiments. The RTS signalsmay be transmitted by an eNB that supports LTE-U (LTE-U eNB). Examplesof such an eNB may be the base stations 105, 105-a, and 105-b of FIG. 1,FIG. 2A, and FIG. 2B, respectively. The CTS signals may be transmittedby a UE that supports LTE-U (LTE-U UE). Examples of such a UE may be theUES 115, 115-a, and 115-b of FIG. 1, FIG. 2A. and FIG. 2B, respectively.

An RTS signal 2005 (or RTS 2005) may be generated and transmitted aftera CCA 720-1 during a subframe 725-j in a current gating interval. Thesubframe 725-j may be an example of the subframe 9 (S′) 725 of FIG. 7.That is, the subframe 725-j may be a last subframe in the current gatinginterval. The RTS 2005 may be transmitted when the CCA 720-1 issuccessful in the middle of the subframe interval. An LTE-U eNB may usethe transmission of the RTS 2005 to hold the channel until the nextsubframe boundary (or beyond).

The RTS 2005 may be compatible with RTS as defined for IEEE 802.11standards (e.g., WiFi). A transmitter address (TA) field of the RTS 2005may include the MAC ID of the transmitting LTE-U eNB. From the MAC ID,other LTE-U nodes (e.g., LTE-U eNBs) of the same deployment mayrecognize this as a “friendly RTS” and not go silent (may follow LTE-UMAC/enhanced intercell interference coordination (eICIC) proceduresinstead). A network allocation vector (NAV) field may be used to reservetime slots, as defined in IEEE 802.11 standards. For example, a NAVfield may reserve at least a next subframe (1 milliseconds period).However, more typically, a NAV field may reserve at least the next 5subframes (up to a maximum consistent with listen-before-talk). Areceiver address (RA) field of the RTS 2005 may contain multiple hashesof cell radio network temporary identifier (C-RNTI) for a set of UEsserved by the LTE-U eNB.

An RTS signal such as the RTS 2005 may be used prior to an UL grant toprotect the subsequent UL transmission. In a standalone deployment, suchas the one described above with respect to FIG. 2B, an RTS signal mayalso be sent prior to a physical downlink shared channel (PDSCH)transmission to protect the subsequent UL subframe where HARQ feedback(ACK/NACK) may be sent by a UE (on the same unlicensed spectrumchannel). In response to an RTS signal, at least the UEs that arereferred to in the RA field of the RTS signal may respond by sending aCTS signal if they are capable of receiving data/signaling from the eNB.Other UEs served by the LTE-U eNB that may wish to send a schedulingrequest (SR) or a pending CSI report may also respond with a CTS signal.Unlike WiFi, the CTS sent by the LTE-U UEs contain the MAC ID of theserving eNB in their TA field. A NAV field in the CTS may be determinedfrom the corresponding RTS signal.

Returning to FIG. 20, the UEs named/served by the transmitting eNB maysend a common CTS signal 2010 (or CTS 2010) a short inter-frame space(SIFS) interval after the RTS 2005. The common CTS 2010 allows the UEsto grab the channel as quickly as possible. In the remaining duration ofsubframe 9, before the next subframe boundary (with subframe 10), theUEs identified by the RTS 2005 may send individual CTS signals 2015 (orCTSs 2015) staggered in time. The staggering may depend on the order inwhich the UEs are identified in the RA field of the RTS 2005. A TA fieldin each of the individual CTSs 2015 may carry a hash of their fullidentity. The individual CTSs 2015 indicate to the eNB that the UEs areready to receive data/grant. The use of individual CTSs 2015 enablebetter scheduling design, more efficient use of the channel by usingFDMA among multiple UEs. After subframe 9, which includes the RTS 2005,the common CTS 2010, and the individual CTSs 2015, a next subframe 710-a(subframe 10) may include transmissions of PDSCH 2020, 2020-a, and2020-b.

FIG. 21 shows a flowchart of a method 2100 for transmitting RTS signalsand receiving CTS signals in an unlicensed spectrum according to variousembodiments. The method 2100 may be implemented using, for example, thebase stations or eNBs 105, 105-a, and 105-b of FIG. 1, FIG. 2A, and FIG.2B, respectively; and/or the system 100 of FIG. 1 and the portions ofthe system 100 of FIG. 2A and FIG. 2B. In one implementation, one of theeNBs 105 may execute one or more sets of codes to control the functionalelements of the eNB 105 to perform the functions described below.

At block 2105, clear channel assessment (CCA) may be performed todetermine the availability of unlicensed spectrum.

At block 2110, an RTS signal (e.g., RTS 2005) may be transmitted to aset of UEs using the unlicensed spectrum when a determination is madethat the unlicensed spectrum is available (e.g., CCA is successful).

At block 2115, a common CTS signal (e.g., CTS 2010) and an individualCTS signal (e.g., CTS 2015) may be received from one or more of the UEsin response to the RTS signal.

The RTS signal may be received at the UEs in the set of UEs over theunlicensed spectrum, and the common CTS signal and a respectiveindividual CTS signal may be transmitted from each UE, over theunlicensed spectrum, in response to the RTS signal.

In some embodiments of the method 2100, transmitting the RTS signalincludes transmitting the RTS signal prior to an uplink grant to protecta subsequent uplink transmission over the unlicensed spectrum, from theset of UEs. The RTS signal may include a MAC ID of a source (e.g., eNB)of the RTS signal. The MAC ID of the source may include a 48-bit MAC ID,for example. The RTS signal may include a hashed version of the MAC IDof the UEs in the set.

In some embodiments of the method 2100, the common CTS signal may bereceived a SIFS after the transmission of the RTS signal and the commonCTS signal may include a MAC ID of the source of the RTS signal. Each ofthe individual CTS signals received may include a MAC ID of the sourceof the RTS signal and a MAC ID of the UE transmitting the individual CTSsignal. The individual CTS signals may be received at staggered times.

In some embodiments of the method 2100, the CCA may be performed duringa subframe of a current gating interval, the RTS signal may betransmitted after the CCA, and the common CTS and individual CTSssignals may be received before an end of the subframe. In someembodiments, a time associated with the CCA and a time associated withthe subsequent transmission of the RTS signal may be randomly staggeredamong different eNBs to avoid collisions at devices receiving the RTSsignal. Moreover, a time associated with the CCA and a time associatedwith the subsequent transmission of the RTS signal may be mutuallystaggered to avoid collisions at devices receiving the RTS signal, thestaggering being based at least on coordinating signaling exchangedbetween eNBs.

Turning next to FIG. 22A, a diagram 2200 is shown that illustrates anexample of virtual CTS (V-CTS) signals in a licensed spectrum accordingto various embodiments. The V-CTS signals may be transmitted by UEs thatsupport LTE-U (LTE-U UE). Examples of such UEs may be the UES 115,115-a, 115-b, and of FIG. 1, FIG. 2A. and FIG. 2B, respectively.

After a DCF interframe space (DIFS) interval, which may include a CCA(e.g., 4 milliseconds) occurring whenever media frees up, an eNB (e.g.,base station 105) may send an RTS signal 2205 (or RTS 2205) in anunlicensed spectrum addressing all UEs (e.g., UE₁, . . . , UE_(n)) ofinterest with NAV. After a SIFS interval, the eNB sends a CTS-to-self inthe unlicensed spectrum. The eNB may immediately schedule downlinktraffic based on current knowledge for the rest of the subframe andcontinue scheduling and ACK 2230. The scheduling may be performed usingthe physical downlink control channel (PDCCH) and the PDSCH in signals2220 and 2225. The UEs addressed by the RTS 2205 may send back, in alicensed spectrum, V-CTS signals 2215 (or V-CTSs 2215) with updatedmeasurements (e.g., RTS/CTS measurements) for the eNB to improve futurescheduling. In this scenario, the CTS signaling takes place virtually orout-of-band (out of the unlicensed spectrum) by concurrently using thelicensed spectrum in LTE-U.

Turning next to FIG. 22B, a diagram 2200-a is shown that illustrates anexample of virtual RTS (V-RTS) signals in a licensed spectrum accordingto various embodiments. The V-RTS signals may be transmitted by eNBsthat support LTE-U (LTE-U eNB). Examples of such eNBs may be the basestations 105, 105-a, and 105-b of FIG. 1, FIG. 2A. and FIG. 2B,respectively.

After a DIFS interval, which may include a CCA (e.g., 4 milliseconds)occurring whenever media frees up, an eNB (e.g., base station 105) maypoll the UEs of interest (e.g., UE₁, . . . , UE_(n)) on a primary cell(PCell) when the media or channel is sensed to be free or available. TheeNB need only send a CTS-to-self signal 2210 (or CTS-to-self 2210) on anunlicensed spectrum to save overhead. The eNB sends a V-RTS signal 2235(or V-RTS 2235) using a licensed spectrum and the UEs addressed by theV-RTS 2235 may respond by each sending a V-CTS 2215-a also in thelicensed spectrum. In this scenario, all the signaling needed for RTSand CTS takes place virtually or out-of-band (out of the unlicensedspectrum) by concurrently using the licensed spectrum in LTE-U. Like thescenario in FIG. 22A, the eNB may proceed to send scheduling informationusing signals 2220 and 2225 (e.g., PDCCH and PDSCH).

FIG. 23 shows a flowchart of a method 2300 for transmitting an RTSsignal or a V-RTS signal according to various embodiments. The method2300 may be implemented using, for example, the base stations or eNBs105, 105-a, and 105-b of FIG. 1, FIG. 2A, and FIG. 2B, respectively;and/or the system 100 of FIG. 1 and the portions of the system 100 ofFIG. 2A and FIG. 2B. In one implementation, one of the eNBs 105 mayexecute one or more sets of codes to control the functional elements ofthe eNB 105 to perform the functions described below.

At block 2305, an RTS signal (e.g., RTS 2205) may be transmitted in anunlicensed spectrum or a V-RTS signal (e.g., RTS 2235) may betransmitted in a licensed spectrum, addressed to a set of UEs (e.g.,UE₁, . . . , UE_(n)).

At block 2310, a CTS-to-self signal may be transmitted in an unlicensedspectrum along with the transmission of the V-RTS signal.

The RTS signal or the V-RTS signal may be received at the UEs in the setof UEs over the unlicensed spectrum.

In some embodiments of the method 2300, a V-CTS signal may be receivedin the licensed spectrum for each of the UEs in the set in response tothe RTS signal or the V-RTS signal. The V-CTS signal may includemeasurements made by the respective UE for use in future scheduling. Insome embodiments, traffic may be scheduled after receiving the V-CTSsignals based on current channel knowledge for a remainder of asubframe. The RTS signal may be transmitted in the downlink primarycomponent carrier.

FIG. 24 shows a flowchart of a method 2400 for receiving V-CTS signalsin response to an RTS signal or a V-RTS signal according to variousembodiments. The method 2400 may be implemented using, for example, thebase stations or eNBs 105, 105-a, and 105-b of FIG. 1, FIG. 2A, and FIG.2B, respectively; and/or the system 100 of FIG. 1 and the portions ofthe system 100 of FIG. 2A and FIG. 2B. In one implementation, one of theeNBs 105 may execute one or more sets of codes to control the functionalelements of the eNB 105 to perform the functions described below.

At block 2405, an RTS signal (e.g., RTS 2205) may be transmitted in anunlicensed spectrum or a V-RTS signal (e.g., RTS 2235) may betransmitted in a licensed spectrum, addressed to a set of UEs (e.g.,UE₁, . . . , UE_(n)).

At block 2410, a CTS-to-self signal may be transmitted in an unlicensedspectrum along with the transmission of the V-RTS signal.

At block 2415, a V-CTS signal may be received in the licensed spectrumfrom each of the UEs in the set in response to the RTS signal or theV-RTS signal.

At block 2420, traffic may be scheduled after receiving the V-CTSsignals based on current channel knowledge for a remainder of asubframe.

The RTS signal or the V-RTS signal may be received at the UEs in the setof UEs over the unlicensed spectrum, and the V-CTS signal may betransmitted from each UE, over the unlicensed spectrum, in response tothe RTS signal or the V-RTS signal.

Turning next to FIG. 25, a diagram 2500 is shown that illustratesexamples of normal and robust subframes in an unlicensed spectrumaccording to various embodiments. The normal and robust subframes may betransmitted by eNBs that support LTE-U (LTE-U eNB). Examples of sucheNBs may be the base stations 105, 105-a, and 105-b of FIG. 1, FIG. 2A.and FIG. 2B, respectively. The normal and robust subframes may be usedby UEs that support LTE-U (LTE-U UE). Examples of such UEs may be theUEs 115, 115-a, and 115-b of FIG. 1, FIG. 2A. and FIG. 2B, respectively.

A normal legacy carrier type (LCT) subframe 2505 is shown. Normal LCTsubframes 2505 may be used for LCT waveforms and may carry time-divisionmultiplexed (TDM) PDCCH and CRS. Also shown is a normal new carrier type(NCT) subframe 2515. Normal NCT subframes 2514 may be used for NCTwaveforms but may not include TDM PDCCH and CRS. Instead, a UE may usechannel state information-reference signals (CSI-RS) for feedback andUE-RS for demodulation. In addition to the normal LCT and NCT subframes,FIG. 25 shows a robust LCT subframe 2510 and a robust NCT subframe 2520.Robust subframes may differ from the normal ones in that they mayinclude additional pilots (e.g., common pilots, eCRS) in comparison tonormal subframes, which may be used to facilitate time-frequencytracking and channel estimation at the UE after a long gated-OFF periodof LTE DL transmissions.

For gated LCT waveforms, SYNC subframes (e.g., subframes carrying PSS,SSS, (possibly) PBCH, in addition to other LTE subchannels) may betransmitted in a subframe index=0 (mod 5). The robust LCT subframes 2510may be transmitted for the first X subframes after a gated-OFF periodthat is greater than Y subframes. The parameters X and Y may vary basedon the structure of the subframes and usage rules, for example. NormalLCT subframes 2505 may be transmitted in all other gated-ON periods.

For gated NCT waveforms, SYNC subframes may be transmitted in a subframeindex=0 (mod 5). The robust NCT subframes 2520 may be transmitted forthe first X subframes after a gated-OFF period that is greater than Ysubframes. The parameters X and Y may vary based on the structure of thesubframes and usage rules, for example. Normal NCT subframes 2515 may betransmitted in all other gated-ON periods.

FIG. 26 shows a flowchart of a method 2600 for transmitting normal orrobust subframes in an unlicensed spectrum according to variousembodiments. The method 2600 may be implemented using, for example, thebase stations or eNBs 105, 105-a, and 105-b of FIG. 1, FIG. 2A, and FIG.2B, respectively; and/or the system 100 of FIG. 1 and the portions ofthe system 100 of FIG. 2A and FIG. 2B.

At block 2605, past transmission activity on an unlicensed spectrum maybe compared to an activity threshold (e.g., a number of gated-ON periodsin the unlicensed spectrum over a time period, a duration of a number ofgated-ON periods in the unlicensed spectrum over a time period, and/or anumber of SYNC subframes transmitted in the unlicensed spectrum over atime period).

At block 2610, a first subframe type (e.g., normal LCT/NCT subframes)may be transmitted in the unlicensed spectrum during a next activetransmission when the past transmission activity is greater than theactivity threshold.

At block 2615, a second subframe type (e.g., robust LCT/NCT subframes)may be transmitted in the unlicensed spectrum during a next activetransmission when the past transmission activity is lesser than theactivity threshold. The second subframe type may include a more robustsubframe type than the first subframe type.

In some embodiments of the method 2600, the first subframe type mayinclude an LCT subframe. In some embodiments, the first subframe typemay include an NCT subframe. In some embodiments, the second subframetype may include an LCT subframe with additional common pilots fortracking and channel estimation. In some embodiments, the secondsubframe type may include an NCT subframe with additional common pilotsfor tracking and channel estimation. The method may include transmittingthe first subframe type in the unlicensed spectrum after a predeterminednumber of transmissions of the second subframe type is identified.

Turning next to FIG. 27, a diagram 2700 is shown that illustratesexamples of Physical Uplink Control Channel (PUCCH) signals and PhysicalUplink Shared Channel (PUSCH) signals for an unlicensed spectrumaccording to various embodiments. The PUCCH and PUSCH signals may behandled by eNBs that support LTE-U (LTE-U eNB). Examples of such eNBsmay be the base stations 105, 105-a, and 105-b of FIG. 1, FIG. 2A. andFIG. 2B, respectively. The PUCCH and PUSCH signals may be handled by UEsthat support LTE-U (LTE-U UE). Examples of such UEs may be the UEs 115,115-a, and 115-b of FIG. 1, FIG. 2A. and FIG. 2B, respectively.

PUCCH and PUSCH signals are typically based on localized frequencydivision multiplexing (LFDM) waveforms that occupy a set of subcarrierswhere a different modulation symbol is sent for each subcarrier or someprecoding is done before sending the frequency domain waveform. Whenusing these waveforms, small amounts of data available to be sent resultin a small portion of the spectrum being occupied. Because oflimitations in transmit power spectral density (TX-PSD), when occupyinga small part of the bandwidth a small amount of power is transmitted. Toget away from that, there may be a need to occupy pretty much the entirewaveform. But if most of the waveform is occupied and does not leave anysubcarriers unused, it may not be possible to multiplex different usersfor a given amount of bandwidth. One approach to address this issue isto have each transmitter interleave its signals so they occupy every1-out-of-every-Nth subcarrier (e.g., 1-out-of-10, 1-out-of-12), therebyleaving many subcarriers in the middle unoccupied. This approach mayincrease the nominal bandwidth occupancy to enable sending the waveformwith a higher power (but still with low enough PSD to meet regulations).Interleaved frequency division multiplexing (IFDM) and interleavedorthogonal frequency division multiplexing (I-OFDM) signals may be usedthat occupy 1-out-of-Nth subcarrier in order to send signals confined tothose subcarriers. In FIG. 25, IFDM waveforms are shown to generatePUCCH signals 2705 and PUSCH signals 2710 for transmission in anunlicensed spectrum. Similarly, I-OFDM waveforms are shown to generatePUCCH signals 2715 and PUSCH signals 2720 for transmission in anunlicensed spectrum.

FIG. 28 shows a flowchart of a method 2800 for generating PUCCH and/orPUSCH signals for an unlicensed spectrum according to variousembodiments. The method 2800 may be implemented using, for example, thebase stations or eNBs 105, 105-a, and 105-b of FIG. 1, FIG. 2A, and FIG.2B, respectively; the UEs 115, 115-a, and 115-b of FIG. 1, FIG. 2A. andFIG. 2B, respectively; and/or the system 100 of FIG. 1 and the portionsof the system 100 of FIG. 2A and FIG. 2B. In one implementation, one ofthe eNBs 105 or one of the UEs 115 may execute one or more sets of codesto control the functional elements of the eNB 105 or the UE 115 toperform the functions described below.

At block 2805, one or both of PUCCH signals and PUSCH signals may begenerated based on interleaved signals that increase nominal bandwidthoccupancy in an unlicensed spectrum.

At block 2810, the generated signals may be transmitted (e.g., by aneNB) in the unlicensed spectrum. In some embodiments, the interleavedsignals may include IFDM signals. In some embodiments, the interleavedsignals may include I-OFDM signals.

One or both of the generated signals may be received in the unlicensedspectrum by, for example, a UE.

Turning next to FIG. 29, a diagram 2900 is shown that illustrates anexample of load-based gating in an unlicensed spectrum according tovarious embodiments. The load-based gating may be performed by eNBs thatsupport LTE-U (LTE-U eNB). Examples of such eNBs may be the basestations 105, 105-a, and 105-b of FIG. 1, FIG. 2A. and FIG. 2B,respectively.

The listen-before-talk (LBT) techniques described above may be used inframe-based equipment (FBE). However, other LBT techniques are alsoavailable that are based on load-based equipment (LBE). The LBT-FBEtechniques rely in part on gating that preserves the 10 millisecondsradio frame structure of LTE. The use of shorter gating structures (1milliseconds, 2 milliseconds), while allowing for periodic gating, tendnot to preserve the LTE frame structure. Using LBT-LBE may provide thepotential benefit of retaining the subframe structure of LTE PHYchannels without the need for symbol puncturing at the beginning or end.However, time-reuse among different LTE-U nodes may no longer be assuredon the same deployment because each eNB uses its own random back-offtime for extended CCA. Therefore, for LBT-LBE, the CCA may be similar tothe CCA for LBT-FBE, but extended CCA (which is not used in LBT-FBE),may be based on randomly selecting an integer N (e.g., 1≤N≤q), andwaiting for N CCA durations where the channel is clear.

The transmission at different subframes (SFs) in a subframe sequencetransmitted in an unlicensed spectrum channel may be based on resultsfrom extended CCAs and from CCA. Extended CCA may be based on aparameter 4≤q≤32, whose value is advertised by the vendor. When thechannel has had a long break, CCA may need to be performed. If CCA findsa clear channel, then it may be possible to start transmitting rightaway. If not, extended CCA may be performed before transmission. Oncetransmission begins, it may continue for at most (13/32)×q msc (referredto as the maximum channel occupancy time), before another extended CCAmay need to be performed. Upon a successful reception (from anothernode), ACK/NACK transmission may begin immediately (without) CCA,provided that the last successful CCA/extended CCA was performed lessthan a maximum channel occupancy time before.

Returning to the example of FIG. 29, the CCA time may be set to 25 μsand q=24, so that the maximum channel occupancy time is approximately9.75 milliseconds. The minimum idle time for extended CCA isapproximately between 25 μs and 0.6 milliseconds. CUBS may be used tofill the gap as described above. In this example, extended CCA 720-m isperformed at subframe (SF) 8 in a sequence 2905. The maximum channeloccupancy time is such that a next extended CCA 720-m need not beperformed until SF18. LTE downlink transmissions may take place duringSFs 9-12 as a result of the channel being free after the first extendedCCA 720-m. Since there is a transmission gap after SF 12, a CCA 720-nmay be performed at SF 15 for additional transmissions within themaximum channel occupancy time. As a result of the CCA 720-n, LTEtransmissions may take place at SFs 16 and 17. As noted above, a secondextended CCA 720-m may occur after the maximum channel occupancy time,which in this example leads to additional LTE transmissions in SFs22-25.

Turning to FIG. 30, a diagram 3000 is shown that illustrates a UE 115-dconfigured for LTE-U. The UE 115-d may have various other configurationsand may be included or be part of a personal computer (e.g., laptopcomputer, netbook computer, tablet computer, etc.), a cellulartelephone, a PDA, a digital video recorder (DVR), an internet appliance,a gaming console, an e-readers, etc. The UE 115-d may have an internalpower supply (not shown), such as a small battery, to facilitate mobileoperation. The station UE 115-d may be an example of the UEs 115, 115-a,115-b, and 115-c of FIG. 1, FIG. 2A, FIG. 2B, and FIG. 16, respectively.The UE 115-d may be configured to implement at least some of thefeatures and functions described above with respect to FIGS. 1-29.

The UE 115-d may include a processor module 3010, a memory module 3020,a transceiver module 3040, antennas 3050, and an UE modes module 3060.Each of these components may be in communication with each other,directly or indirectly, over one or more buses 3005.

The memory module 3020 may include random access memory (RAM) andread-only memory (ROM). The memory module 3020 may storecomputer-readable, computer-executable software (SW) code 3025containing instructions that are configured to, when executed, cause theprocessor module 3010 to perform various functions described herein forusing LTE-based communications in an unlicensed spectrum. Alternatively,the software code 3025 may not be directly executable by the processormodule 3010 but be configured to cause the computer (e.g., when compiledand executed) to perform functions described herein.

The processor module 3010 may include an intelligent hardware device,e.g., a central processing unit (CPU), a microcontroller, anapplication-specific integrated circuit (ASIC), etc. The processormodule 3010 may process information received through the transceivermodule 3040 and/or to be sent to the transceiver module 3040 fortransmission through the antennas 3050. The processor module 3010 mayhandle, alone or in connection with the UE modes module 3060, variousaspects of using LTE-based communications in an unlicensedspectrum.

The transceiver module 3040 may be configured to communicatebi-directionally with base stations (e.g., base stations 105). Thetransceiver module 3040 may be implemented as one or more transmittermodules and one or more separate receiver modules. The transceivermodule 3040 may support communications in a licensed spectrum (e.g.,LTE) and in an unlicensed spectrum (e.g., LTE-U). The transceiver module3040 may include a modem configured to modulate the packets and providethe modulated packets to the antennas 3050 for transmission, and todemodulate packets received from the antennas 3050. While the UE 115-dmay include a single antenna, there may be embodiments in which the UE115-d may include multiple antennas 3050.

According to the architecture of FIG. 30, the UE 115-d may furtherinclude a communications management module 3030. The communicationsmanagement module 3030 may manage communications with various accesspoints. The communications management module 3030 may be a component ofthe UE 115-d in communication with some or all of the other componentsof the UE 115-d over the one or more buses 3005. Alternatively,functionality of the communications management module 3030 may beimplemented as a component of the transceiver module 3040, as a computerprogram product, and/or as one or more controller elements of theprocessor module 3010.

The UE modes module 3060 may be configured to perform and/or controlsome or all of the functions or aspects described in FIGS. 1-29 relatedto using LTE-based communications in an unlicensed spectrum. Forexample, the UE modes module 3060 may be configured to support asupplemental downlink mode, a carrier aggregation mode, and/or astandalone mode of operation in an unlicensed spectrum. The UE modesmodule 3060 may include an LTE module 3061 configured to handle LTEcommunications, an LTE unlicensed module 3062 configured to handle LTE-Ucommunications, and an unlicensed module 3063 configured to handlecommunications other than LTE-U in an unlicensed spectrum. The UE modesmodule 3060, or portions of it, may be a processor. Moreover, some orall of the functionality of the UE modes module 3060 may be performed bythe processor module 3010 and/or in connection with the processor 3010.

Turning to FIG. 31, a diagram 3100 is shown that illustrates a basestation or eNB 105-d configured for LTE-U. In some embodiments, the basestation 105-d may be an example of the base stations 105, 105-a, 105-b,and 105-c of FIG. 1, FIG. 2A, FIG. 2B, and FIG. 16, respectively. Thebase station 105-d may be configured to implement at least some of thefeatures and functions described above with respect to FIGS. 1-29. Thebase station 105-d may include a processor module 3110, a memory module3120, a transceiver module 3130, antennas 3140, and a base station modesmodule 3190. The base station 105-d may also include one or both of abase station communications module 3160 and a network communicationsmodule 3170. Each of these components may be in communication with eachother, directly or indirectly, over one or more buses 3105.

The memory module 3120 may include RAM and ROM. The memory module 3120may also store computer-readable, computer-executable software (SW) code3125 containing instructions that are configured to, when executed,cause the processor module 3110 to perform various functions describedherein for using LTE-based communications in an unlicensed spectrum.Alternatively, the software code 3125 may not be directly executable bythe processor module 3110 but be configured to cause the computer, e.g.,when compiled and executed, to perform functions described herein.

The processor module 3110 may include an intelligent hardware device,e.g., a CPU, a microcontroller, an ASIC, etc. The processor module 3110may process information received through the transceiver module 3130,the base station communications module 3160, and/or the networkcommunications module 3170. The processor module 3110 may also processinformation to be sent to the transceiver module 3130 for transmissionthrough the antennas 3140, to the base station communications module3160, and/or to the network communications module 3170. The processormodule 3110 may handle, alone or in connection with the base stationmodes module 3190, various aspects of using LTE-based communications inan unlicensed spectrum.

The transceiver module 3130 may include a modem configured to modulatethe packets and provide the modulated packets to the antennas 3140 fortransmission, and to demodulate packets received from the antennas 3140.The transceiver module 3130 may be implemented as one or moretransmitter modules and one or more separate receiver modules. Thetransceiver module 3130 may support communications in a licensedspectrum (e.g., LTE) and in an unlicensed spectrum (e.g., LTE-U). Thetransceiver module 3130 may be configured to communicatebi-directionally, via the antennas 3140, with one or more UEs 115 asillustrated in FIG. 1, FIG. 2A, FIG. 2B, and FIG. 16, for example. Thebase station 105-d may typically include multiple antennas 3140 (e.g.,an antenna array). The base station 105-d may communicate with a corenetwork 130-a through the network communications module 3170. The corenetwork 130-a may be an example of the core network 130 of FIG. 1. Thebase station 105-d may communicate with other base stations, such as thebase station 105-e and the base station 105-f, using the base stationcommunications module 3160.

According to the architecture of FIG. 31, the base station 105-d mayfurther include a communications management module 3150. Thecommunications management module 3150 may manage communications withstations and/or other devices. The communications management module 3150may be in communication with some or all of the other components of thebase station 105-d via the bus or buses 3105. Alternatively,functionality of the communications management module 3150 may beimplemented as a component of the transceiver module 3130, as a computerprogram product, and/or as one or more controller elements of theprocessor module 3110.

The base station modes module 3190 may be configured to perform and/orcontrol some or all of the functions or aspects described in FIGS. 1-29related to using LTE-based communications in an unlicensed spectrum. Forexample, the base station modes module 3190 may be configured to supporta supplemental downlink mode, a carrier aggregation mode, and/or astandalone mode of operation in an unlicensed spectrum. The base stationmodes module 3190 may include an LTE module 3191 configured to handleLTE communications, an LTE unlicensed module 3192 configured to handleLTE-U communications, and an unlicensed module 3193 configured to handlecommunications other than LTE-U in an unlicensed spectrum. The basestation modes module 3190, or portions of it, may be a processor.Moreover, some or all of the functionality of the base station modesmodule 3190 may be performed by the processor module 3110 and/or inconnection with the processor 3110.

Turning next to FIG. 32, a block diagram of a multiple-inputmultiple-output (MIMO) communication system 3200 is shown including abase station 105-g and a user equipment or UE 115-e. The base station105-g and the UE 115-e may support LTE-based communications using anunlicensed spectrum (LTE-U). The base station 105-g may be an example ofthe base stations 105, 105-a, 105-b, and 105-c of FIG. 1, FIG. 2A, FIG.2B, and FIG. 16, while the UE 115-e may be an example of the UE 115,115-a, 115-b, and 115-c of FIG. 1, FIG. 2A, FIG. 2B, and FIG. 16. Thesystem 3200 may illustrate aspects of the system 100 of FIG. 1 andaspects of the portions of the system 100 shown in FIG. 2A and FIG. 2B.

The base station 105-g may be equipped with antennas 3234-a through3234-x, and the UE 115-e may be equipped with antennas 3252-a through3252-n. In the system 3200, the base station 105-g may be able to senddata over multiple communication links at the same time. Eachcommunication link may be called a “layer” and the “rank” of thecommunication link may indicate the number of layers used forcommunication. For example, in a 2×2 MIMO system where base station 800transmits two “layers,” the rank of the communication link between thebase station 105-g and the UE 115-e is two.

At the base station 105-g, a transmit (Tx) processor 3220 may receivedata from a data source. The transmit processor 3220 may process thedata. The transmit processor 3220 may also generate reference symbols,and a cell-specific reference signal. A transmit (Tx) MIMO processor3230 may perform spatial processing (e.g., precoding) on data symbols,control symbols, and/or reference symbols, if applicable, and mayprovide output symbol streams to the transmit modulators 3232-a through3232-x. Each modulator 3232 may process a respective output symbolstream (e.g., for OFDM, etc.) to obtain an output sample stream. Eachmodulator 3232 may further process (e.g., convert to analog, amplify,filter, and upconvert) the output sample stream to obtain a downlink(DL) signal. In one example, DL signals from modulators 3232-a through3232-x may be transmitted via the antennas 3234-a through 3234-x,respectively.

At the UE 115-e, the antennas 3252-a through 3252-n may receive the DLsignals from the base station 105-g and may provide the received signalsto the demodulators 3254-a through 3254-n, respectively. Eachdemodulator 3254 may condition (e.g., filter, amplify, downconvert, anddigitize) a respective received signal to obtain input samples. Eachdemodulator 3254 may further process the input samples (e.g., for OFDM,etc.) to obtain received symbols. A MIMO detector 3256 may obtainreceived symbols from all the demodulators 3254-a through 3254-n,perform MIMO detection on the received symbols if applicable, andprovide detected symbols. A receive (Rx) processor 3258 may process(e.g., demodulate, deinterleave, and decode) the detected symbols,providing decoded data for the UE 115-e to a data output, and providedecoded control information to a processor 3280, or memory 3282. Theprocessor 3280 may include a module or function 3281 that may performvarious functions related to using LTE-based communications in anunlicensed spectrum. For example, the module or function 3281 mayperform some or all of the functions described above with reference tothe FIGS. 1-29.

On the uplink (UL), at the UE 115-e, a transmit (Tx) processor 3264 mayreceive and process data from a data source. The transmit processor 3264may also generate reference symbols for a reference signal. The symbolsfrom the transmit processor 3264 may be precoded by a transmit (Tx) MIMOprocessor 3266 if applicable, further processed by the demodulators3254-a through 3254-n (e.g., for SC-FDMA, etc.), and be transmitted tothe base station 105-g in accordance with the transmission parametersreceived from the base station 105-g. At the base station 105-g, the ULsignals from the UE 115-e may be received by the antennas 3234,processed by the demodulators 3232, detected by a MIMO detector 3236 ifapplicable, and further processed by a receive processor. The receive(Rx) processor 3238 may provide decoded data to a data output and to theprocessor 3240. The processor 3240 may include a module or function 3241that may perform various aspects related to using LTE-basedcommunications in an unlicensed spectrum. For example, the module orfunction 3241 may perform some or all of the functions described abovewith reference to FIGS. 1-29.

The components of the base station 105-g may, individually orcollectively, be implemented with one or more Application SpecificIntegrated Circuits (ASICs) adapted to perform some or all of theapplicable functions in hardware. Each of the noted modules may be ameans for performing one or more functions related to operation of thesystem 3200. Similarly, the components of the UE 115-e may, individuallyor collectively, be implemented with one or more Application SpecificIntegrated Circuits (ASICs) adapted to perform some or all of theapplicable functions in hardware. Each of the noted components may be ameans for performing one or more functions related to operation of thesystem 3200.

It should be noted that the various methods described in flowcharts arejust one implementation and that the operations of those methods may berearranged or otherwise modified such that other implementations arepossible.

The detailed description set forth above in connection with the appendeddrawings describes exemplary embodiments and does not represent the onlyembodiments that may be implemented or that are within the scope of theclaims. The term “exemplary” used throughout this description means“serving as an example, instance, or illustration,” and not “preferred”or “advantageous over other embodiments.” The detailed descriptionincludes specific details for the purpose of providing an understandingof the described techniques. These techniques, however, may be practicedwithout these specific details. In some instances, well-known structuresand devices are shown in block diagram form in order to avoid obscuringthe concepts of the described embodiments.

Information and signals may be represented using any of a variety ofdifferent technologies and techniques. For example, data, instructions,commands, information, signals, bits, symbols, and chips that may bereferenced throughout the above description may be represented byvoltages, currents, electromagnetic waves, magnetic fields or particles,optical fields or particles, or any combination thereof.

The various illustrative blocks and modules described in connection withthe disclosure herein may be implemented or performed with ageneral-purpose processor, a digital signal processor (DSP), anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA) or other programmable logic device, discrete gate ortransistor logic, discrete hardware components, or any combinationthereof designed to perform the functions described herein. Ageneral-purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, multiple microprocessors, one or moremicroprocessors in conjunction with a DSP core, or any other suchconfiguration.

The functions described herein may be implemented in hardware, softwareexecuted by a processor, firmware, or any combination thereof. Ifimplemented in software executed by a processor, the functions may bestored on or transmitted over as one or more instructions or code on acomputer-readable medium. Other examples and implementations are withinthe scope and spirit of the disclosure and appended claims. For example,due to the nature of software, functions described above can beimplemented using software executed by a processor, hardware, firmware,hardwiring, or combinations of any of these. Features implementingfunctions may also be physically located at various positions, includingbeing distributed such that portions of functions are implemented atdifferent physical locations. Also, as used herein, including in theclaims, “or” as used in a list of items prefaced by “at least one of”indicates a disjunctive list such that, for example, a list of “at leastone of A, B, or C” means A or B or C or AB or AC or BC or ABC (i.e., Aand B and C).

Computer-readable media includes both computer storage media andcommunication media including any medium that facilitates transfer of acomputer program from one place to another. A storage medium may be anyavailable medium that can be accessed by a general purpose or specialpurpose computer. By way of example, and not limitation,computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or otheroptical disk storage, magnetic disk storage or other magnetic storagedevices, or any other medium that can be used to carry or store desiredprogram code means in the form of instructions or data structures andthat can be accessed by a general-purpose or special-purpose computer,or a general-purpose or special-purpose processor. Also, any connectionis properly termed a computer-readable medium. For example, if thesoftware is transmitted from a website, server, or other remote sourceusing a coaxial cable, fiber optic cable, twisted pair, digitalsubscriber line (DSL), or wireless technologies such as infrared, radio,and microwave, then the coaxial cable, fiber optic cable, twisted pair,DSL, or wireless technologies such as infrared, radio, and microwave areincluded in the definition of medium. Disk and disc, as used herein,include compact disc (CD), laser disc, optical disc, digital versatiledisc (DVD), floppy disk and blu-ray disc where disks usually reproducedata magnetically, while discs reproduce data optically with lasers.Combinations of the above are also included within the scope ofcomputer-readable media.

The previous description of the disclosure is provided to enable aperson skilled in the art to make or use the disclosure. Variousmodifications to the disclosure will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other variations without departing from the spirit or scopeof the disclosure. Throughout this disclosure the term “example” or“exemplary” indicates an example or instance and does not imply orrequire any preference for the noted example. Thus, the disclosure isnot to be limited to the examples and designs described herein but is tobe accorded the widest scope consistent with the principles and novelfeatures disclosed herein.

What is claimed is:
 1. A method for wireless communications, comprising:aligning a clear channel assessment (CCA) period in time across aplurality of base stations, wherein a duration of the CCA period is thesame for each of the plurality of base stations; selecting, from thealigned CCA period, a timing for performing a CCA; performing the CCA atthe selected timing in a current gating interval to determine whether anunlicensed spectrum is available for a transmission in a nexttransmission interval; and gating OFF the transmission in the unlicensedspectrum for the next transmission interval when the unlicensed spectrumis determined to be unavailable.
 2. The method of claim 1, wherein thetransmission includes a downlink transmission.
 3. The method of claim 1,wherein the transmission includes an uplink transmission.
 4. The methodof claim 1, wherein the plurality of base stations include a pluralityof evolved Node Bs (eNBs).
 5. The method of claim 1, wherein the CCAperiod is aligned across a plurality of evolved Node Bs (eNBs) fromdifferent operators.
 6. The method of claim 1, wherein the CCA isperformed during a last subframe of the current gating interval.
 7. Themethod of claim 1, wherein the CCA is performed during a first subframeof the current gating interval.
 8. An apparatus for wirelesscommunications, comprising: means for aligning a clear channelassessment (CCA) period in time across a plurality of base stations,wherein a duration of the CCA period is the same for each of theplurality of base stations; means for selecting, from the aligned CCAperiod, a timing for performing a CCA; means for performing the CCA atthe selected timing in a current gating interval to determine whether anunlicensed spectrum is available for a transmission in the unlicensedspectrum for a next transmission interval; and means for gating OFF thetransmission in the unlicensed spectrum for the next transmissioninterval when the unlicensed spectrum is determined to be unavailable.9. The apparatus of claim 8, wherein the transmission includes adownlink transmission.
 10. The apparatus of claim 8, wherein thetransmission includes an uplink transmission.
 11. The apparatus of claim8, wherein the plurality of base stations include a plurality of evolvedNode Bs (eNBs).
 12. The apparatus of claim 8, wherein the CCA period isaligned across a plurality of evolved Node Bs (eNBs) from differentoperators.
 13. The apparatus of claim 8, wherein the CCA is performedduring a last subframe of the current gating interval.
 14. The apparatusof claim 8, wherein the CCA is performed during a first subframe of thecurrent gating interval.
 15. An apparatus for wireless communications,comprising: a processor; memory in electronic communication with theprocessor; and instructions stored in the memory, the instructions beingexecutable by the processor to: align a clear channel assessment (CCA)period in time across a plurality of base stations, wherein a durationof the CCA period is the same for each of the plurality of basestations; select, from the aligned CCA period, a timing for performing aCCA; perform the CCA at the selected timing in a current gating intervalto determine whether an unlicensed spectrum is available for atransmission in the unlicensed spectrum for a next transmissioninterval; and gate OFF the transmission in the unlicensed spectrum forthe next transmission interval when the unlicensed spectrum isdetermined to be unavailable.
 16. The apparatus of claim 15, wherein thetransmission includes a downlink transmission.
 17. The apparatus ofclaim 15, wherein the transmission includes an uplink transmission. 18.The apparatus of claim 15, wherein the plurality of base stationsinclude a plurality of evolved Node Bs (eNBs).
 19. The apparatus ofclaim 15, wherein the CCA period is aligned across a plurality ofevolved Node Bs (eNBs) from different operators.
 20. The apparatus ofclaim 15, wherein the CCA is performed during a last subframe of thecurrent gating interval.
 21. The apparatus of claim 15, wherein the CCAis performed during a first subframe of the current gating interval. 22.A non-transitory computer-readable medium comprising instructionsexecutable by a processor to cause a wireless communications apparatusto: align a clear channel assessment (CCA) period in time across aplurality of base stations, wherein a duration of the CCA period is thesame for each of the plurality of base stations; select, from thealigned CCA period, a timing for performing a CCA; perform the CCA atthe selected timing in a current gating interval to determine whether anunlicensed spectrum is available for a transmission in the unlicensedspectrum for a next transmission interval; and gate OFF the transmissionin the unlicensed spectrum for the next transmission interval when theunlicensed spectrum is determined to be unavailable.
 23. Thenon-transitory computer-readable medium of claim 22, wherein thetransmission includes a downlink transmission.
 24. The non-transitorycomputer-readable medium of claim 22, wherein the transmission includesan uplink transmission.
 25. The non-transitory computer-readable mediumof claim 22, wherein the plurality of base stations include a pluralityof evolved Node Bs (eNBs).
 26. The non-transitory computer-readablemedium of claim 22, wherein the CCA period is aligned across a pluralityof evolved Node Bs (eNBs) from different operators.
 27. Thenon-transitory computer-readable medium of claim 22, wherein the CCA isperformed during a last subframe of the current gating interval.
 28. Thenon-transitory computer-readable medium of claim 22, wherein the CCA isperformed during a first subframe of the current gating interval.